My lower back hurt for a time, so I started spending 3 minutes a day in the squatting posture used the world over for people live with dirt floors, or who spend a lot of time outside. Actually, that is the posture used in much of the world for crapping. I remember visiting a bathroom in Geneva with running water, but which had two foot pedestals in the middle of a giant basis. You squatted, did your business, then flushed the whole thing down.
In any event, it worked. And it has changed the quality of my sleep for the better. I can’t say how, merely that it is different. The night seems more open somehow. I first noticed this sleeping on hotel room floors while traveling with my kids when they were littler.
I do sometimes miss softer beds, and do sometimes get them when I travel, but this practice is on the whole salubrious. The Buddhists made it a point to sleep on hard surfaces. One can see this as a sort of asceticism, but there may be a practical reason as well, one conducive to inner work in some way I am not prepared to speculate on at the moment.