Darwin gets hot pretty easily, and we just have him sleep on the plastic bottom in his crate for that reason. But when he's just lounging around, he finds ANYTHING that is soft to lay on. Ideally, a blanket, pillows, sweatshirt, or towel. But if none of that is available, he will actually lay on top of stray socks, hand towels, or even a pair of pants that are on the floor. You will never see him laying on bare carpet if some random "softie" is available. It is surprising because of how easily he gets hot... you would think he would just lay on the cold kitchen tile!
Toby loves to lay on towels. Especially damp bath towels! I have a hard time keeping fresh/clean hand towels next to the bathroom sink because he always steals them to lay on them. :)