I've seen a bunch of posts on light and sleep here, but nothing detailed re. mattresses. I ran across this which might prove valuable to future searchers, re. a modular approach to sleep design: https://www.reddit.com/r/Mattress/comments/otdqms/diy_mattresses_an_introductory_guide/
I'd also be curious to hear if others find this to be epistemically sound. Given the value of sleep, having a process for efficiently finding a near ideal sleep surface (or at least one which doesn't cause pain) seems rather important.