Mattresses aren't the only thing you can sleep on. I'd consider picking up and installing a hammock - they're not only cheap (~$100 for a top of the line one, $10 and 2 hours for making your own), but they also give you significantly more usable living space.
Yes, they may be more space-efficient, but isn't it more important whether they damage your sleep quality?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.