When back packers carry a sleeping pad, it's not only about sleeping on something slightly less hard and rugged than the bare ground. It's also about not getting hypo-thermia -- you know, freezing. The ground is always going to be colder than you. So as you lie on the ground, the ground makes you lose heat -- and your body probably can't make more heat fast enough to keep up with what you are losing to the cold ground. If this goes on long enough, you can DIE from the heat loss. That's what "freezing to death" is, losing your body heat faster than you can make more heat.
So put some kind of thermal insulation between your body and the ground. It can be a foam pad made for camping, newspapers, rugs, blankets, a pet bed, whatever. It doesn't have to be "solid stuff." The air spaces between two rugs are insulative too. An air mat, even a small one for the beach, is insulative.