K has been in her twin sz mattress for a month or so and she 'rolls' out every now and then. we had to put it on the floor since she climbed her crib AND the converted toddler bed it was crazy!
I would get the side rails until she gets used to it they have many choices from metal ones, plastic one's and inflatable ones. not sure which one we will get K i gues we will see how she does when her 'platform' bed arrives