We co-sleep. He won't sleep without me at night (unless it's been a realllly long day for both of us).
At nap time, he sleeps in his swing.
We usually don't swaddle him unless he's acting like he wants to be swaddled (it's weird to say that I know, but sometimes we can just tell...). When he's in the swing, I put him in, then tuck a blanket really tight around him (sort of like swaddling, except he could get out pretty easily if he really wanted to).
Have you tried having some white noise for him to sleep with? Like a fan or a heater? I use a heater only because we are living in my mom's basement right now, and it's freezing down here, even with a blanket. I would be using a fan if it was summer or if it was the first level of the house.
Also, my husband's cousin puts her children on their stomachs to sleep. She doesn't worry about it for some reason though...