Disclaimer: I know this is feasible because this is my tiny 300 sq. ft. NYC apartment! We came up with this space-saving solution because our ceilings are only 10 feet high. In the top photo, you see that the bed slides out from underneath the platform on casters. When the bed is fully tucked away, there's a step attached so you can climb onto the platform easily. In the bottom photo, you see the living room area we eventually arranged on top.

And yes, we wallpapered the floor.