We have a matress on the floor and it has worked out pretty well. I always tried to center him in the middle of the mattress to lessen the chance of falling off. We also have carpet, so if he did fall off, it wasn't a big deal. Also, keep the bedding to a minimum - we just used a fitted sheet - I am also always paranoid of SIDS and never used pillows. When he was older and could crawl around, he often fell asleep on the floor and I would just move him back when I went to bed.