When we took down my son's crib and upgraded him to a toddler bed, we would often go in and check on him after he had fallen asleep. A lot of the time we would find him rolled over to the side with his head leaning ON the little safety railing. The bed is made of metal, sounds comfortable, I know...
My husband mentioned that we should put something over it, immediately I knew what I should do...
I went to the dollar store and got a pool noodle. I let my son pick out whatever color he wanted. He felt like such a helper :). I brought the noodle home and put it up against the bar, and cut it to the right length.