A safety rail might help by making it harder to get out of bed and maybe less worth the effort. We put our 21 month old in a big boy bed recently but it's a loft bed so it has a railing all the way around it (and a ladder/slide at the end). The first week he kept getting out repeatedly. I didn't mind if he stayed in the bed and sat there quietly playing with his toys as he would eventully get tired and go to sleep, but whenever he got out I would just pick him up and quietly put him back. He got out of bed a lot at first and cried when I put him back, but it gradually got less and less as he learned it was a waste of time to get out, and now he stays in it all night.