hammocks
Hammocks are fun, but highly uncomfortable if you need to turn at night. Almost impossible. Nevertheless, I slept all night in one in Cass, W.Va. during a rafting trip in the winter. (Yes, you can raft in the winter)
I nestled inside a thick sleeping bag which made turning easier - a nylon womb more or less, which made it slippery.
On my stomach, my back arched badly - it constantly hurt to stay in that position for more than five minutes.
My friends thought it was funny. During the night, when we set up the sleeping arrangements in below zero weather, I had inadvertently tied one end of my hammock to a stout sign post. It said, "No Camping".
By the way, camping in hammocks on vertical rock faces is de rigeur in some places.