Hi Christy,
We had the problem of side rails when transitioning to the toddler bed setting of our girl's cribs, too. There are SOME convertable cribs now that come with the attachment to add, but most still don't, and we found that the bed was too high for a "toddler bed" without a rail. Most people seem to be pointing out that the problem with the regular bed rails is that they need a boxspring. I think that the real problem is that they go the entire length of the crib, making it no different than having you son in the crib with the side down...not actually a safe option. If he has to climb out of the toddler bed over a rail, he can still get hurt (and he would have a much more difficult time climbing back in after he runs around the room playing). Also, the side rail wouldn't be as sturdy as the rail he was climbing over, so he AND it could go over.
My girls are both very petite, so we opted to get them regular toddler beds (low to the ground, and with rails going 1/2 way down the sides) instead of going straight to big girl beds with the rails. I wouldn't recommend this unless your son is small enough to be expected to fit comfortably on his crib mattress for another 2-3years. If he is big enough to easily climb in and out of a twin bed, go that route with the safety rail. As far as sleeping on the floor, my oldest was the one that was always on the floor (I had to push her aside with the door to get in the room <g>). Just pick him up before you go to bed, and put him in his bed for the night. She loved the freedom of the toddler bed so much at first, that it was a party every night (she and her sister share a room and switched to the toddler beds at the same time). After a month or two, we stopped finding her on the floor (started finding her in her sisters bed instead, but that is another story). A year later she will still pull her pillow down and make a little bed behind the chair in her room like a little camp...it's fun.
Good luck with the bed transition. I thought that the convertable crib was the BEST idea since I had two and wouldn't need to get toddler beds. Boy, was I wrong...
S.