Arms up swaddle - transition??

I’m really stressed as my son (just turned 4 months) is showing signs he might roll soon. He sleeps in the nested bean arms up swaddle and sleeps through the night. I have tried to take one arm out during naps but he wakes himself up with his arms moving so much. He’s such a good sleeper with the arms up swaddle and I’m panicked he won’t adjust with arms out. I’ve tried the Merlin but he really didn’t like that. Any suggestions on transitioning? Since he sleeps so well now I’m stressed that I have to even take his arms out of the arms up swaddle ☹️ help!!