Swaddling

So my little guy (3 weeks) is not a huge fan of being swaddled and the majority of the time he gets his arms out!  He sleeps fine like that in the Rock and play but when he's in the bassinet and his arms are out he gets startled.  Anyone have any suggestions on sleep sacks or anything else that works well for sleeping and not having to be swaddled. I want to start putting him in his crib for naps but I know he will get his arms out and wake himself up!