K.D.
Have you tired a sleep positioner with the swaddle? We haven't used one but I think that's what they're made for. Even if you don't use one, I think the thing is to just stick with it and he will get used to sleeping on his back. It's the safest way. However, once he learns to roll over all bets are off. There's nothing you can do then. But the risk of SIDS is greatly reduced by then anyway. Personally, I'd be really nervous co-sleeping and having him on his tummy too. We co-slept with our daughter until she learned to roll over. At that point I was too nervous about her sufficating so she started sleeping in her crib. Good luck.