My baby is 3 1/2 months now and sleeping in her own bed but we co-slept until about 5 weeks when she started sleeping 8 to 9 hours a night.
Anyway, for my own peace of mind I laid DD in a sleep positioner right next to me, the positioner was against my belly so it gave me comfort that I wouldn't roll onto her, which I think maternal intincts help with that alot anyway.
However, a friend of mind wasn't so confident so she bought one of these
http://www.amazon.com/exec/obidos/tg...=baby&n=542338 and she really likes it. However by the time she showed it to me DD was 3 weeks old and sleeping at least a 5 hour stretch every night so I didn't see the point in paying $50 for something I didn't see me using but for a couple more weeks, which would have been the case in my situation. However, her baby is 29 days older and she is still having to breastfeed her little guy at least 2 times a night so she is still using it.
So I guess it really depends on your situation.