The big problem for me, concerning a plain "air mattress", is that you body never heats it up in the winter. And in the summer heat you need more than a little padding to let your body ventilate.
Stitchawl, I'm assuming that the Japanese futon is thin so that it can be cleared away when not in use?
The ones here, I'm sure you've seen them, are made up of a great many layers of quilted cotton. Somehow, though, it doesn't feel like sleeping on 6 to 8 inches of layered sheets. They're very comfortable winter or summer.
The two most uncomfortable places I ever slept were in an elevator mechanical room on top of an apartment building, and totally unprepared night in the woods in winter. Both long boring stories.
Strangely enough I've never had a problem sleeping on the ground while backpacking. And I just remembered sleeping under a highway overpass when it was inconvenient to set up camp during a heavy rain.
Nice, high, and dry. But very noisy.
