That's how all beds were made prior to the advent of box springs (or modern mattresses, which don't require a separate box spring). Very old beds still have the hooks necessary to hold up the ropes that supported the mattress.
I've seen medieval beds in the UK that were a wooden 'tray' (on legs, or built into a wall) and the guides said a hessian bag was filled with straw (dried stems of wheat/corn/barley; straw and hay are often used interchangeably though, so it might have been dried wild grasses) for bedding.
I assumed poor people slept on the floor with whatever coverings they could muster. Suspended beds seem very decadent.
The stretched fabric, like canvas, over a rectangular frame design seems pretty common and would have surely been a more natural early bed. Similarly hammocks - which I thought were common on ships (at least in the later middle ages).
Guess I've discovered I'd like to read a history of beds!
