One of the most surprisingly comfortable surfaces I've ever reclined on was in a teepee-like Sami structure in Sweden's Arctic Circle. The "floor" was thickly layered with birch branches covered in reindeer hides. The dense collection of branches provided a surprising amount of spring and bounce; it was like lounging on an enormous circular bed, and opened my eyes to the fact that you needn't sleep on a mattress to be comfortable.
Speaking of which, Gothenburg-based Wranne Fahraeus Design (working in conjunction with Chalmers University) has designed a mattress-free bed made of upholstered sprung steel, shown above.
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