hi boomba
we co-sleep as well, and we have taken one of the sides off the cot and pulled it right up next to our bed. dp has tied rope securely around the base of the cot and our bed so that it is really tight and there is no gap between the cot and the bed, if that makes sense??
it means that ds can be right up next to us but gives us all more room and ds can't fall out. usually he falls asleep in our bed snuggled up under my arm and then i quietly move him into the cot. so far it seems to work really well..
We ended up doing the same thing, mainly to give us some more room in bed. Oddly enough we had no issue with DD crawling off the bed as she liked to sleep close. She was more of a concern if we had to leave the room, as she would roll anywhere then. So the sidecar cot helped to stop that, as all she could do was roll around in the cot and had to physically crawl up to get to the main bed.