This cell bed is really just a glorified steel shelf with a waterproof cushion pretending to be a mattress isn’t it? Only the most uncomfortable furnitures for this project!
I haven’t made a ladder but it should still work fine for double bunking. That being said… two people in 9 square meters might be pushing just a little bit.
The mattress was the part that got me worried the most. Initially I was gonna make something more “normal” but I figured that this would most likely be the “minimum” you’d get in a cell of that style, and blankets if you are nice. I suppose the rubbery aspect might be a plus for some.