They don't mind sleeping on the ground. My Budo pancakes himself on his basking rock to soak up the remaining heat at night. Once the basking rock is no longer keeping him warm, I tuck him in. He has claimed several of my shirts and sweaters and one of my bathrobes, along with other miscellanious clothes and blankets around the house.
Here's a pic of him after watching a late-night movie with me. He looked so chilly all by himself, and my bed is too high up to have him sleep with me, so I made him a cozy bed of his own.