Search for floor poufs (example). The range from foam blocks, to pillows, to leather bags you can store clothes in and also sit on.

I have a weighted blanket that sounds like it would also fit your situation, serving two purposes as a chair and blanket. They're fleece for comfort, but beaded that it gives you space between the cold floor. Storage could be difficult though, depending on how strong you are and how small you need this thing to roll up. I have a twin that's about 6" tall and 1.75 ft. wide when folded to a sit-able size.