bottom sags in mattress

Hello–

I was in a hurry to change mattresses because of some back and hip pain I had started experiencing with my old mattress. When looking for a new mattress ran into the following issue: when I lie on my back on a mattress, my core sinks lower than the rest of my body, enough that it is uncomfortable. Basically I feel like my butt has sunk and my legs and head are higher than my pelvis. Following the guidance on this site I tried >30 different mattresses in stores including some that were innerspring with varying firmness of cotton/foam or pillowtop or memory foam layers on top, foam core with latex top, foam core with memory foam on top, zoned innerspring core with memory foam and latex on top, all latex. The same thing happened with all mattresses I tried, although the problem was least with an innerspring mattress that had a very firm comfort layer of foam/cotton on top. Since I had so much trouble finding something that was even remotely comfortable and I was having a lot of pain, I went ahead and bought this “ultra-firm” mattress. I decided not to do a mail-order because I was nervous ordering something I hadn’t tried when I needed something quickly that would be helpful and I had so little luck with everything that I had found.

Now that I am not in such a state of crisis, I am wondering if I could do better. For reference, I am 5’ 6", recently weighted at 127 lbs, and sleep in all positions but lately has only been back and side because I can’t get comfortable at all on my stomach. Wondered if it is because I have been working out so my weight has shifted to where it is now pretty much all in my core and a bit denser, but the rest of my body isn’t heavy enough to sink into the mattress. Mattresses with a memory foam top were the worst among those I tried.

Is this an issue you have run into with other customers? Any suggestions?

Thank you!