Yes hammocks were known. The problem of having them set up right, and the problem of getting out of them if attacked seems to be reasons for them not catching on in the woods. They are also pretty cold when cool air circulates under them, and historically they worked well in Cuba and SE Asia, probably due to the climate.
You mentioned air mattress and foam..., so I suspect that you are not talking about a trek? So..., how about a straw-tick?
Buy five yards of ticking material, the same used for pillows, and patching round ball and such. Fold it in half width-wise, and sew up one side. Measure the width of your shoulders, trim it up to that width plus 1/2", and sew a 1/2" wide seam on the other side. You should now have a cloth bag, sewed on both sides, with an open end, and 6' 6" long. This is the "tick".
At an event, you take half of a standard bale of straw, take handfuls of the straw, and add it to the inside of the tick, losely, as you don't want hard clumps. A half bale is all you want. Use a leather thong to tie up the open end, and then shake the tick to evenly distribute the straw on the inside. Lay the tick on the ground, and lie on it to pack it down. You will have a comfortable "mattress", that is correct, and insulates quite well.
I used mine this past weekend in the cold and damp at Ft. Fred, and only needed my matchcoat, and a thin British military surplus blanket, plus a knit cap, and was toasty warm in 40 degree temps.
When done, you dump out the straw, and roll up the tick until the next event. You can launder it if needed.
Use the remainder of the cloth that you cut off for round-ball patching or for other projects.
LD