my DS was a side sleeper. he had fairly bad reflux - and i found for him that if he vomited in his sleep that on his side it would just pour out, but on his back he'd choke on it 0_0 even now he wont sleep on his back (unless co-sleeping) but do what your mummy instinct tells you. to make sure DS didnt roll over i used to put him in the recovery position with a sheet tucked firmly eather side of him to help stop the rolling, once he started to roll on his own but struggled to roll back again i rolled up a small face washer and tucked it in under his arm/against his chest, stopping him from rolling onto his face. but even now (at almost 12 months old) he'd rather sleep on his side.