After quite a bit of research, I settled on the Summer Infant WrapSack. It's as easy to use as the SwaddleMe, but doesn't constrain his legs, and has a zipper for easy nighttime diaper changes (of course, at 9 weeks, we now finally rarely need to change his diaper at night!)
It's a bit wide, as we purchased the size Large which is designed for babies 14lbs+ and Wyatt is just under 11lbs. However, after a wash and a trip to the dryer, its actually not much wider than the HALO newborn swaddle we've been using up until now, and we're still able to tie him tightly enough in it for it to be safe. Here he is peacefully sleeping with one arm out.
|Summer Infant WrapSack|