As an osteopath the people I treat most often at festivals for back pain are those who use air beds. They are followed in numbers by those who use folding camp beds.
Having, over the years, spent over 1000 nights under canvas, in both multi-occupant and one-man tents, I would always sleep directly on the ground using spare jumpers under my sleeping bag for insulation. Use a mallet to make a dent in the ground for your shoulder and another for your hip. Perfectly warm, no pains or discomfort.

Colyn.