I slept for three years on a slab of concrete with a folded wool fire blanket as a mattress. On top of it I had sheets and a top blanket and a regular pillow. My roommates thought I was crazy, but after a few days of adjusting to it, I found it to be the most comfortable sleep I had experienced up until that time. All back pain disappeared. That was thirty years ago. I sleep on a regular American bed now, but any time I’ve had any issue with back pain or core muscle strain, I think back on that concrete slab with fond memories.

I'm sure there are lots of people who would benefit from sleeping on their back on a firm surface. I have mild positional sleep apnea. When I sleep on my back I stop breathing a few times an hour. Sleeping on my back might improve some things but isn't good for me having a restful nights sleep.

I remember a few years ago a designer/researcher (Japanese if I remember) came up with a bean-bag type bed that they claimed was a more natural fit for the way humans sleep evolutionarily.

If I search for that now I get either mattress 'review' sites (aka sales channels), or kinky videos.

edit: aha, found it: https://www.theguardian.com/world/2016/jun/21/chimpanzees-be...

Whenever I have back pain, I switch to sleeping on a foam camping pad on the floor. Works great, but annoys the wife

When I was in China for a few months, the hardness of the bed surprised me. The mattress, such as it was, was just a plywood box covered in a thin layer of ticking.

I found it extremely difficult.to find a comfortable sleeping position. Never got used to it.

Bodyweight seems like a major factor never discussed when looking at mattresses or sleeping positions. As a teen I remember the point where a sleeping bag on a wooden floor stopped being comfortable.

Body can can sleep well anywhere if tired enough. Problem is trying to sleep when you're not, especially if you have difficulties falling asleeping.