ThermaRest is your friend. MSR was kind enough to donate one the first trip to Africa
for the falcons I was working with. (We'd bought other gear
that they sold at dealer's cost for us, but there wasn't budget
for a $80 air mattress. They knew the value of it and sent one for me anyway.) I've slept on it on rocks, sticks, and even at home when my back bothers me. Though it's only an inch thick, it's about the most comfortable thing overall to sleep on. Keeps ya insulated from heat and cold as well. Highly recommended!