Swaddling transition

Hi all, need some advice! My LO is going to be 4 months on the 26th of this month. He has been swaddled for sleeping (naps and nighttime) since about a month old. It is the ONLY way he will sleep. He hasn’t started rolling over on his own yet but he’s REALLY close! I’m so worried about trying to get him out of the swaddle because I just know he won’t sleep (he sleeps through the night so I’m spoiled). We use the SwaddleMe swaddles and he sometimes can get his arms out of it. Anytime I’ve tried leaving an arm out he just rubs his face or sucks his fingers endlessly. Help!!