J.W.
I know your problem. We just converted our daughters bed and it is the same way. We ended up getting one of those mesh things I believe you are talking about that say not for use with a Toddler bed. I'm pretty sure the reason for that is they are afraid the mattress is not strong enough. But there is an anchor thing on it that goes under the bed with the rails. And it didn't work at first and she fell out of the bed twice while she was sleeping. Luckily with the bed being so much lower to the ground it wasn't a big deal. We ended up tying the anchor and looping the cord all around the rails on the bed. Trust me that thing dosent' budge anymore. I made sure of it. Plus, you can push it to the front of the bed and still have a place for them to crawl in and out of bed easily. We got ours at Babies R Us. Good Luck.