I have had mild back pain all my life and often felt stiff getting up in the morning. A while back I moved to a yoga mat (both to be more minimalist and because I thought it would help my back) and missed the padding for a few days, then I was fine. I then started sleeping on the floor with only a sheet under me and it now feels even better. The only two things I feel I need are a normal sized pillow and I do like to use one of those large bamboo pillows that you hold between your legs while on your side.
Right now when I sleep I feel some sort of relief as my back flattens against the hard floor.
For naps or lounging like sitting on a couch reading with a dog, I like them really soft.
What about you guys?
I don't sleep, but I like to lay flat on my back for 10-15 minutes a few times a week. People weren't made to sit a desk. Gotta stretch the back out or I get sore and get the hunchback hump for a few days until I stretch it out again.