I slept on the floor for years. Finally built myself a "raised floor" (queen-sized platform at low bed height, but no mattress) to get up out of the dust and dogs. I love it.
Mattresses -- yes, even the really good posturepedic ones -- just don't cut it for me.
Seems to me that we'd get less creaky with age if we did more getting up and down from hard and low surfaces, and if we didn't coddle our bodies with cushioning on every side.