It was some years ago when we were selling Ballonbeds at the Saunders Lakeland Mountain Marathon that someone said "What I need is a lightweight pillow!"
After a little researching we found the perfect answer: A balloon pillow. It's basically a torus (doughnut) shaped balloon that will lay flat on the ground.
You can blow this balloon up by mouth and tie it off with a small piece of string that we provide. This means that you can re-use it again and again.
You need to first inflate it to about the size of a car tyre and then deflate it to the size you want in order to achieve the perfect torus (and stable) shape.