Advice - transition to bed

Hi ladies...I hope some of you have some great words of wisdom for me.  So, we took the front off Aiden's crib this weekend (to turn it into a toddler bed) and now it doesn't have any sort of rails.  We put padding down on the floor just in case, and it's a good thing we did because he's fallen out several times and then rolls all around his room.  The first night we'd put him back in his bed, but stopped because we didn't want him to keep falling out. But I feel terrible he's pretty much sleeping on the floor.  We have his "big boy" bed set up in the other room and we've put a rail on it, but I'm a little nervous for him to sleep there because it's pretty high off the ground for him.(I'm really regretting getting this bed now) He has to use a step to get in and out.

I realize he's a little young, but I'm trying to slowly transition him so I can get the nursery set up for DC#2 due in 4 months. I didn't want him to feel like he was getting kicked out of his room once the baby arrived.  Did your kids fall out of bed so much? What did you do about this? I'm pretty much open to anything at this point.  Thanks!