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You need some. They make an awesome bed. Slit the corners and lay a layer or two down, and it is as good as if not better than a mattress.
You think I'm joking. I prefer it.
If you insist on a mattress, just lay a layer of thin box-stuff on it.
Proof: "Boxes are made for sleeping" delivered. Shutting down. *fzz-oop!*