We use two comforters -- one on the bottom and one on the top. The bottom one is down and it was given to us so I'm not sure if it's a twin or full. I *think* it's a full. The one we put over us is Queen size and is made out of wool (got it while I was living in Australia). We stay very warm, even in below-freezing temps and we've got so many covers, it feels really cozy. It'd be nice to have sheets, but it'd be too much of a pain to take down and put back every day (we like to use the dinette during the day) so we take this simpler route.
Personally, I think we could use some extra padding to sleep on but for now, it'll do as-is. If we were to upgrade to a 5th wheel for longer trips, I'd need a more proper mattress or some more foam. I know Tuft and Needle used to make a 5" mattress or maybe someone out there makes an 8" deep one. I'd do as others have -- use a bread knife to cut it and cover it in some jersey.
Has anyone given Beddy's a try? I think a full size would fit the deluxe-sized beds but I'm not sure about the standard. From what I can tell, they're all the rage these days and look pretty slick if you ask me. Like a Trav a Sac but a little more finished looking. And for the price... they better be!
https://beddys.com/