Hi mnmeater,
OK … that removes both of these as possible issues.
This depends on the person. It would make some difference yes but some would feel it and some wouldn’t … at least initially…
There are two basic functions of a mattress which are comfort / pressure relief and support / alignment.
Comfort is what you feel when you first lie on a mattress or go to sleep at night and support is generally what you feel when you wake up in the morning either with or without back discomfort and pain.
Much of the initial “comfort” and pressure relief you feel on a mattress comes from the top layer or top few inches. While comfort is very subjective and varies with each person and their body type and sleeping style (and medical and physiological issues) … soft is usually considered to be in the range of about 24 ILD. Below this is plush or ultra plush (which is what you have)
There are also two types of “support”.
Primary support is what “stops” your pelvic girdle from sinking past the comfort layers too far and comes from the deeper firmer support layers (the polyfoam support layer in your mattress)
Secondary support comes from the thickness and softness of the comfort layers which need to “allow” the pressure points of the body to sink in far enough to relieve pressure but they also fill in the recessed gaps in your sleeping positions at the same time and help maintain the alignment of the inward curves or recesses of the body or spine. They determine how much travel distance you have to sink into softer materials before your heavier pelvic girdle is “stopped” by the deeper primary support layers.
The middle or “transition” layer contributes to both to different degrees depending on its firmness and plays a dual role.
Different sleeping positions have different requirements and back sleepers typically need thinner comfort layers than side sleepers because there are less pressure points on your back and the recessed gaps are shallower which means you don’t need as much softer materials to relieve pressure and fill in the gaps and being closer to the support layers can help prevent the heavier pelvis from sinking in too far and putting the spine out of alignment.
So how much your pelvis sinks down into the mattress (too far is usually the typical cause of lower back issues) is controlled by the firmness of the support layer and the thickness and softness of the comfort layers.
Your bottom support layer (for primary support) is probably fine so the odds say that your comfort layers are too thick and soft for a back sleeper which means that your heavier parts have too far to “travel” before they are “stopped” by the support layers. The normal thinking would be that you need one layer of soft material for pressure relief (just a little firmer than the 14 but still one step below soft) and then a firmer middle layer which will help more with support and a little less with pressure relief (because most people similar to you wouldn’t need more than 3" of soft material and some back sleepers only need 2"). Both of these firmness increases will help improve secondary support and help your pelvis to sink in less. This would still be on the soft/thick side for a many back sleepers but it would be an improvement if the issue you are facing is connected to the overall support of the mattress (which is likely) rather than being a medical issue where any “averages” don’t apply.
This would give you 9" of soft latex on top (24 is considered “soft” and 19 is considered “plush” and 14 is considered “ultra plush) so this would be very risky yes because of the thickness of soft foam in the upper layers of the mattress. In effect the bottom part of the 9” would be so deep it would be part of your primary support layer this would be a very soft support layer. You would be a long way away and your pelvis would have a long way to “travel” before it was “stopped” by the firmer layers below it. I would keep the comfort layers a little thinner and softer on in the top layer (for pressure relief) and firmer in the middle and underneath (for support) and then if you needed just a little extra pressure relief (which would be unusual for a back sleeper) perhaps add a thin topper if you need just a bit more pressure relief.
I would also keep in mind that you may be completely outside of any averages because of your back issues and each person can be very different in their physiology or makeup (which is why what woks well for one person may be completely unsuitable for you even if they have a similar body type and sleeping style and why I would avoid what may work for someone else unless they are very much like you in body type, sleeping style, physiology, sensitivity, age, and health issues).
So while only your own experience can really know how well something will work for you in “real life” … your experience may be pointing the way at least to the most likely direction of changes that may help and this will at least give you a sense of the types of changes that may be beneficial to you based on your symptoms (assuming again that they are not caused by medical issues that could cause you to be much more sensitive to either pressure relief or support issues than most people) and which types of changes have the highest odds of success.
If for some reason that is connected to your “unique” circumstances you are in a “lower probability group” and weren’t as sensitive to support issues or a layer combination that would not work well for most people and a combination that was very much outside the norm would work better for you (such as the 2 layers of 24 and a layer of 14 on top of that which would normally be a very risky construction for most people), then you could achieve that with 2 x 24 ILD 3" layers on your side of the mattress and then adding a 14 ILD topper (either on your side alone or across the whole mattress). It may feel very “comfortable” … but you may also find that if you sleep on it for a while that your back aches are becoming more common.
Post #2 here (along the same lines and with a different set of complicating factors) may also be worth reading and it’s also important to make sure that you test each change in layer combination for long enough (at least a few days) to make sure that what you experience is a pattern and more indicative of your longer term experience on that combination and not just the result of any change itself that your body may need some time to catch up to or other factors that can affect short term experience.
All of this is “educated” guesswork though and in the end only you can know through your own experience what works for you and what doesn’t … especially when there are some “complicating” factors and these suggestions are only based on which changes would have the highest probability of working for most people.
Phoenix