We took my son out of the crib at 13 mo. We placed his crib mattress on a large piece of plywood, cut to fit the twin be frame. We already had the frame. We then took him comforter and padded it around the mattress so that if he did roll out, he didn't hit the board and edge of the rails. He slept this way for 1.5 years before we put a twin mattress on the bed.
Yes, we did eventually put a bed rail on the mattress as well as the twin mattress.
There is no magical age at when to remove a child from the crib. Each child is different. Mine was 1 when I found him sitting on the dresser after climbing out of his crib! The crib was gone as soon as we could...within the month!
I would put the mattress on the floor, lacking a bedframe to put it in. Nothing wrong with sleeping on the floor-if he rolls out, it's only 6 inches down. I would not waste money on a toddler 'bed' they don't last that long.
Safety should always be first....he'll get use to sleeping out of the crib. And soon enough, you'll sleep better!
Good luck!