Yeah I have the same challenge now that my little one learned how to crawl!
My husband and I bought two barriers at Toys R Us and put one on each side. I also have a baby monitor cause I know as soon as he gives a little squeal of delight, I better run. He's a fast crawler!
Having the mattress on the ground is a safe precaution, but I think our babies can outsmart us, so there's nothing like constant supervision.
Good luck!
Karla

We co-sleep with our daughter - now 17 months - and have done since she was around 3 months before which she was in a **********.

Initially I just kept the ********** pushed up against my side of the bed and then once she started getting mobile I put a barrier on (which her first response to was to pull up on it and threaten to launch herself over it)!

We never put the mattress on the floor as our flat is small and there just isn't the space. Instead I put a row of hardish pillows down the middle of the bed and made a nest space between them and the barrier. She's not much of a mover when she's asleep and we had a baby alarm so I could get in fast when she woke up.

She rolled out of the bed twice when she was about 8/9 months and had been mountaineering over the pillows but didn't do more than give herself a shock. I had bought rubber shock absorber sports mats and put them either side so that there was some level of protection as we have wooden floors.

I taught her to climb out safely and then we bought a little set of steps from IKEA and now she climbs in and out of our bed with no problems.

It is one of the bits that really worried me at the beginning but in practice it was fine.

My son has been sleeping in the family bed since day one. When he became mobile we taught him to crawl off the bed feet first. He could crawl off the bed before he could walk. He has only fallen off the bed once and that was cause he was jumping around acting like a monkey!

Good question! My 11 month old will either sit up, roll around, or crawl to the edge of the bed before he really wakes up or makes a sound. Even though we are in a small apartment, I have a baby monitor so I can check on him the moment I hear rustling or his breathing change. He hasn't fallen out of bed yet! Also, when he's awake we spend time on the bed (changing dipes, playing, etc.). One time my husband caught him as he crawled off the bed. I think it scared my son to have a brief sensation of falling, even though he ended up safely in dad's arms. Now, everytime he gets close to the edge I say, "Careful, you're going to fall and hurt yourself". I am always within arm's reach, but he will look over the edge and seems to sort of get that he does NOT want to go over. Lots of surrounding pillows & blankets are also a good idea!