A.S.
When my son was young I got one of these:
http://www.snugtuckpillow.com/how_it_works.htm
It is wonderful. No hard metal rail, but also the assurance that the baby will not fall off the bed. When he nursed on one side I kept him in the middle of the bed between me and my hubby, the other side, I had the snugtuck pillow. Now I use it on his "big boy bed" instead of a rail. He can climb over it, but if he rolls towards it while sleeping, it keeps him on the bed. I also had a flat pillow that he slept on and we always scooched down further in the bed so that the covers could cover us, but not so much him. Hope this helps!