I was chatting with my friend who made me a DIY UQ (now named my Thunder Quilt, pictures to follow) and one thing led to another and the idea of a Winter only hammock broke into consciousness.
If you used the concept of a double (or triple but let's stick to double for now) layer hammock and put a durable reflective material (space blanket-ish) between them that would work. Make it the same size as the hammock except where trimming is needed to gather the ends, etc. Now you put a few stitches here and there to keep the reflective surface in place and you have something. I think you would have to add just a bit of extra reflective material to help with the hammock stretch to make it comfortable but you get the idea.
To take this further you can do the same with other material, anything you want. Of course you can still put your normal UQ under when you hang.