Hi Tereci.
Welcome to our Mattress Forum! 
Thanks for sharing your stats and Mattress history,
Sealy doesn’t list the mattress information you need to know to be able to compare the quality of the materials and components to the mattress durability guidelines and determine the useful life of this mattress. Now that this mattress is in your court it may be worth it to you to determine what’s wrong with it and to attempt to fix it for any period of time that is likely to last.
First off, the LÖNSET slatted bed base with its closely spaced slats seems to be quite sturdy but I am not sure that the flexible slats are recommended for this particular mattress. A flexible slat system under a mattress can change the feel and response of the mattress compared to a rigid non-flexing or semi-flex support system which can be either neutral (meaning you can’t feel the difference), detrimental, or beneficial depending on which combination is the best match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). A flexible slat foundation is an “active” part of a sleeping system just like any of the other layers or components in the mattress itself that compress or flexes under your weight but the only way to know whether it would be better or worse for you (or whether you could feel any difference) would be based on your own personal experience (you could compare your mattress with flexible slats underneath it to the same mattress on the floor to see how much effect the slats would have). If you feel any improvement then it is possible that the support system is the cause of your discomfort … or … there is a combination of faulty/flexing foundation and the too soft or too firm support layers.
Your “thought process” is correct … the lower back pain in the morning is usually an indication of poor spinal alignment due to sinking too deeply into the mattress/topper combo or any mattress construction that is not supportive enough or far too firm for your primary sleeping position. This is confirmed by your pains diminishing when taking off the topper and “pain disappearing” when traveling to Europe for a month. Once you removed the topper you also started experiencing shoulder and neck pressure points along with a milder version of lower back pain, all of which may have several causes that need a bit of thinking through.
Only you can determine this by considering a few interrelated factors I’ll be listing below
When you are dealing with pressure relief issues (typically numbness, tingling, limbs falling asleep, etc) then it’s usually about the thickness and softness of the upper layers of your mattress and the “cradle” that is formed when you sink IN to the top layers. If the more “pointy” parts of your body are bearing too much weight (what are called “bony prominences”) then you would have pressure issues because the parts of your body with more surface area would not be in firm enough contact with the mattress and would be bearing too little weight to relieve the pressure on your bony prominences.
When you are dealing with alignment issues (often lower back issues) … then it’s usually about some part of your body sinking DOWN into the mattress too far relative to the others. This can be the result of either
- support layers (such as an innerspring) being too soft or ….
- about comfort layers that are too thick and soft which can allow some parts of the body to “travel” too far.
- It can also be from comfort layers that are too thin or firm or …
- support layers that are too firm where the “gaps” in your sleeping profile (such as under the lumbar curve or waist) aren’t being filled in and supported which can also allow the more recessed parts of the body to sag or “travel” too far. These can both lead to pain and discomfort in either the back or joints when either the spine or joints are outside of their “neutral” alignment.
The flexible slatted bed frame you referenced is bowed and this may change the way the mattress was designed to work which is why I suggested you place the mattress on the floor to see if you can get a few more data points. The Topper from Kohl’s is 1.5" of convoluted memory gel foam of unknown density and IFD so I’d put all in perspective by looking at how the thickness and softness of the topper affected the bed with and without the flexible slatted bed. It would be helpful to know long have you had this mattress in order to determine if it is possible that there is some sag from foams that started to break down.
When testing for support or comfort it is good to know that a mattress is always a balancing act between the need to “allow” the lighter parts of the body (such as the shoulders and upper body) to sink in enough into the upper layers (for pressure relief) and “stop” the heavier parts of the body (primarily the hips/pelvis) from sinking down too far into the deeper layers so that your spine is in good alignment. If the upper body is “held up” too much by the upper layers or the lower parts of the torso and pelvis are “allowed” to sink in too far with support layers that are too soft or thick then the resulting misalignment can lead to back discomfort and pain (which is most noticeable when you wake up in the morning). The layering and design that accomplishes this “balancing act” will depend on the body type, sleeping positions, and personal preferences. As a general guideline … side sleepers need thicker softer upper layers. Back sleepers need something “in-between” and stomach sleepers need thinner firmer upper layers for best alignment.
So “support” primarily comes from a combination of the firmness of the deeper layers and the thickness of the comfort layers (how far away from the deeper firmer layer you are) while pressure relief comes primarily from the softness and thickness of the comfort layers. This is why the comfort layers need to be “just soft and thick enough” to provide good pressure relief in the most “pressure prone” sleeping position (usually the side for those who sleep in this position) but more than “just enough” can put you too far away from the support layers and not “stop” your pelvic girdle from sinking down far enough.
When you use a topper over a mattress two things will happen. The first is it will compress and in combination with the layers below it will take on the shape of your body profile. Softer toppers will compress more than firmer toppers. This “cradle” formed by the upper layers re-distributes weight away from the pressure points of the body. The second is it will “bend” into any softer foam below it. This “bending” will happen more if the topper is firmer than the layers below
TESTING FOR PRESSURE RELIEF OR ALIGNMENT
Firstly, it’s important when you are testing for pressure relief or alignment to make sure you lie on a mattress for long enough that your mind and muscles are fully relaxed. A mattress can feel very different when you are fully relaxed than it does when you are tense. For most people, this means spending at least 15 minutes on a mattress that you are seriously considering and focus on the relaxed feeling that you have when you are going to sleep.
The second key is to focus specifically on testing for alignment and its symptoms rather than comfort in all your sleeping positions. There are several things here that can help.
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Try to sense whether your muscles are able to completely “let go” and allow the mattress to support your natural alignment rather than using muscle tension to keep you in alignment. This means that you can sense your body and muscles fully relaxing without a tendency for any area to be tense.
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Next is to pay particular attention to any tension or discomfort (or even pain) in the areas where poor alignment tends to produce symptoms for you. This can be different for different people but is usually in the lower back or lumbar curve, and the upper back and neck where the spine also curves. Test in all your sleeping positions making sure to move slowly when you change position and stay relaxed. Bear in mind that minor discomfort when you are testing can be amplified when you are sleeping for longer periods of time.
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Next is to make sure that all the inner curves of the spine are filled in so that there are no “gaps” in-between your body and the mattress. It should be fairly difficult to slide your hand under the lower back or waist (if the mattress is too firm then this area will not be filled in well enough and sliding a hand under it will not have enough resistance and will be too easy).
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Finally, you can use the help of someone who can see you on the mattress to make sure there are no obvious issues of alignment such as those in some of the diagrams you provided. If you stand up with “good posture” then your “helper” will be able to get a sense of your natural curves from the side and back and this can help them see if your posture is close to what it is when you are standing up and whether any part of your body is sinking in a little too far (usually the hips/ pelvis) or not enough (usually the upper body and shoulders). They can also make sure that your head and neck is also in good alignment when you are testing because this can affect how a mattress feels in the upper body area.
On your side … your spine should be “relatively” straight (like it is when you look at someone from behind) and your body profile along the side of your body should be similar to your standing position (shoulders and hips in roughly the same relative position). On your back … the spine and body profile should be similar to the side view when you are standing with no obvious areas where parts of you are sagging or sinking in too far or not enough (within reason).
Alignment itself is quite complex and involves different factors. The most important is spinal alignment from top to bottom of the spine and maintaining the natural curvature of the spine however it also involves “side to side” and “rotational” alignment and the alignment of the joints all of which can have a “natural” or “neutral” position along with a “learned” position. All of these interact with the ability of a layer to redistribute weight throughout the surface of the body in each sleeping position (and there are many variations of the 3 basic positions).
Hopefully, after you have a chance to look at these aspects, you’ll have a clearer picture if this mattress is worth fixing (at least for a limited period of time)
Phoenix