I didn't mean to come off quite as extreme as sleeping on the ground. I would be in a sleeping bag and almost certainly in a tent. And I did specify warm weather. In cold conditions you certainly need an insulating pad. Although,40 years and more ago, that consisted of my spare clothing.

In any cases my examples were meant simply as examples, not specific recommendations. My interest is in recovering some of the abilities that are natural to human beings but tend to be lost in Western culture. With the aim of increasing overall comfort, not decreasing it.
I'm 64. It's taken me a little more than a year to become comfortable squatting flat footed. It's useful sometimes on wet ground. An unexpected benefit is that gently and gradually stretching the ligaments seems to have helped my knees.
btw squatting on raised heels can injure the knees. The natural way is flat-footed.