OK … lets take a look at what might be happening so that we can identify the probable cause … and of course increase the odds that a potential solution may work for you. While this may be a little long … I thought it may be more helpful to share my thinking process and the rationale behind it than give you a more “this might fix it” type of answer.
I’m assuming first of all that once you solved the shoulder problems with the pillow … that when you first started using the Tempurpedic you didn’t have either the hip pain or the backache?
A few questions that would help as well …
Can you give me a rough idea of how long ago the hip pain started to happen?
Did you you sleep on your back before (with or without pain) or is back sleeping only recent as a response to the hip pain?
The specs of the mattress are always an important part of any issue so in the case of the Tempurpedic Deluxe they are … Deluxe are 1.2" of softer 5.3 lb memory foam over 2.8" of firmer 5.3 lb memory foam over 2 layers of egg crate polyfoam.
Side sleepers generally need thicker comfort layers but the smaller you are and the lighter the weight … the thinner the foam would need to be. “Just enough” is the key word and this mattress may have a little too much memory foam for your body shape, size, and side sleeping position. It would almost certainly be too much for back sleeping (which needs thinner comfort layers) as it would allow the heavier pelvis to sink in too far into the memory foam and the softer egg crate foam below it while the upper body didn’t. This is the typical cause of lower back pain (not supportive enough under the pelvis and lower back).
Memory foam will soften over time with an initial more rapid softening followed by a more gradual softening followed by breakdown (impressions that don’t come back to level with no weight on the mattress). The initial softening usually happens over the first few weeks and is often called the “break in” period which so many people talk about. This can be sped up by walking on the mattress and breaking open the thin windows in the internal structure of the memory foam.
It seems (pending your reply to the questions at the beginning) that after the initial softening period you were still fine with no hip or back symptoms. This tells me that the 5.3 lb memory foam was allowing your shoulders and hips to sink in far enough to relieve pressure but not so far that there was an alignment issue. It seems to me that as the foam gradually softened … that your hips started sinking in further on your side which could lead to the hips (rather than the spine) being out of alignment and that this may cause joint stress in the hips (a sideways “V” position). The reason that this is more likely than actual pressure problems is that the likelihood of pressure issues with 4" of softened memory foam with eggcrate polyfoam underneath is not so high. It the memory foam layer was thinner and had softened and there was a firmer support layer underneath it that you were feeling “through” the memory foam, then likelihood of a pressure issue would be greater.
So it appears to me that on either side of the mattress … there is just too much memory foam to keep your pelvis and lower back in alignment when you are on your back. It also seems that with the slightly firmer (hasn’t softened yet) foam on the unused side … that the memory foam is still firm enough to keep your hips in reasonable alignment when you are on your side (similar to when you first got the mattress and were (I’m assuming?) symptom free).
There is also a possibility that your hips are a little less flexible than they were 6 years ago and that the amount of misalignment was “within tolerance” then but isn’t any more. In other words the mattress had a little too much memory foam all along for your weight/height and shape when you were sleeping on your side but there were no hip pain symptoms of the slight misalignment 6 years ago. This would account for the hip pain now on the “new and firmer” side when you didn’t have it at the beginning when both sides were new and firmer. On the side where there are more “bony protrusions” … the hips will sink in more easily because the weight is on less surface area but your legs will still be up higher so the leg and hip joint will be bent inwards.
So on to possible solutions … which are difficult because it is more difficult to “fix” a mattress that is too soft and/or thick on top than it is to fix a mattress that is too firm and thin on top.
The good news is that you can affect the ability of memory foam to soften in response to heat by adding a thin layer on top of it that helps to isolate the memory foam from your body heat. This can be a layer of “non memory” foam (such as polyfoam or latex) or a wool or cotton mattress pad as examples. The effect of this will be that the foam will not sink in as far which could help with the alignment issues and the pain both on your side and on your back. The down side of this is that it may only delay how long it takes for the heat to reach the memory foam and the time that it takes to sink in over the course of the night. The odds are also good that even if the hips are fixed by holding them up a little more (the memory foam stays a little cooler) … that it may not fix the back sleeping issues (which I assume is new because until the hip pain you didn’t sleep on your back much?). This is because there is more “excess thickness” for back sleeping than there is for side sleeping.
So I would probably test this theory in a way that if it fails you haven’t spent much and whatever you did spend was refundable which of course means buying from a place like WalMart, Costco, or Sams Club etc. This way if the theory doesn’t pan out … it will tell you that it may be time to look at other options.
A thin latex topper (say 1") would help isolate you from the memory foam but the danger would be that it would only delay how long it took to sink in too far over the course of the night rather than stop it. The latex topper in other words would need to decrease the amount you sunk into the memory foam more than it it allowed you to sink into the new topper.
Looking at the 3 big box stores … it seems WalMart has the best options …
Robot or human? This is a low density soft 1.5" polyfoam topper. It is slightly firmer under the hips than in other areas which may help keeping them up higher. It is soft so it would allow some extra sinking in but it may also stop the memory foam from sinking in more than it “allows”. This would be a good low cost way to test the theory and it is also soft enough that it wouldn’t be too firm and add a new pressure issue.
Robot or human? This is a low cost cotton mattress pad which may help to keep your hips up by reducing the amount the memory foam softened while it would also have some softness itself.
Robot or human? This is a slightly thicker Dunlop latex topper which would isolate you from the memory foam even more. the “risk” here is that the foam itself may be a little on the firm side so while it may help with how much you sink into the memory foam … it may be a little on the firm side for the best pressure relief (it would somewhat take over the pressure relieving job from the memory foam). This would be a good choice if it was soft enough and is a good price and no risk.
A couple of wool options include …
http://www.woolenmill.com/sections/Natures_Comfort_Wool-Filled_Bedding/category.php?category=64&subcategory=0&subsubcategory=0 Also offers very nice thicker wool mattress pads which apparently are refundable and would be ideal if they worked (wool provides a very nice sleeping environment which regulates temperature). Check their return policy to make sure it is refundable after use if you decide to go in this direction.
https://www.amazon.com/SnugFleece-Deluxe-Wool-Mattress-Pad/dp/B001A1TUKY Another thicker wool mattress pad which says it is refundable (as long as it’s not washed) but check to make sure of the exact policy.
So I would try one (or more) of these options before you go in the direction of a new mattress since your Tempurpedic is not (or at least shouldn’t be) at the end of its useful life.
If you do decide to do a bit of shopping in the San Diego area to see what mattress options there are … then post #2 here includes some better options in the area.