We coslept until DS was 10.5 months so he was well mobile for the last few months (he’s in a cot in his own room now). I used to put pillows all around the edge of the mattress with DS right in the middle of the bed. We have quite a small house so it was easy for me to be near the bedroom keeping an eye on him and in easy earshot of any little noise, and still get stuff done around the house while he was asleep. The pillows didn’t stop him from falling off the bed. They were just there as a diversion that would buy me a few extra moments so I could get to him before he crawled away and fell off. It was only a few weeks after he first started crawling that he seemed to learn about edges and falling so it really wasn’t that much of a problem. Sometimes I would watch him to see what he would do, rather than go in and get him straight away, and he would crawl to the edge and look over and he never did fall off the bed.