I have two kids, and co-slept with them from the very beginning. I can honestly say that there is no way you can just roll over onto your baby and smother her, unless you are seriously intoxicated (with drugs or alcohol) or perhaps very obese. When you cosleep, or even if you don't, you will wake up as soon as your baby starts making any kind of noise.
Cosleeping can be a wonderful way to make night feedings easier, and if you and your baby both like being close to each other, it also allows more sleep for everyone. You eliminate the need to get up to nurse, and get the baby to to sleep afterward. Here are some tips to make cosleeping as safe as possible, if you are considering sharing your dreams with your baby:Make sure you have a large bed, with plenty of space for all of you. If possible, push one end of the bed against the wall to make sure your baby can't fall off. There are also pillows like the humanity bed that keep your baby from falling off. If your partner is a heavy sleeper, you may want to put your baby next to you but not next to your partner. Some men are less aware of tiny babies in the bed than mothers. This statement is politically incorrect, but true. Don't smoke or drink alcohol. Don't do drugs. You shouldn't be doing that anyway, but it certainly makes cosleeping unsafe too. Make sure heavy blankets and pillows are not anywhere near your baby. Our solution has been to have the baby on the wall-end of the bed, in a baby sleeping bag, and to not have the duvet cover the baby at all. The same goes for pillows.