If I could fit my comforter in the washing machine, I would get a regular comforter for the guest room. My comforter is a regular one, I pay $20 to get it cleaned once in a while. My guest futon has a duvet since that needs to be cleaned more often and I find it a pain and the cover just doesnt look as neat as a regular comforter.
If I have firmer mattress id do a foam topper, then a mattress pad. Right now I just have a mattress pad. I also need a heavy blanket and sheet, even in the summer. In the winter sometimes I need to add a thin blanket.