I highly recommend the “Love to Dream Transition swaddle”. You can unzip the arms and keep their arms out once they start to roll. Our baby boy also still has a lot of Moro Reflex that startles him awake. Apparently it goes away sometime between month 4-6 for most babies. We also have the Zipadee Zip which everyone recommends. It does help the Moro Reflex if it’s snuggle around the waste. The problem we had with it is that our baby is a giant and kinda thinner. 27in and 17lbs 13oz. So he can’t extend his legs in the size that is snug on his waist. What we did instead is use a Nanit breathing band for our Nanit camera to keep him snug in the next size up.
Transition swaddles! The magic Merlin is truly magic, but recommended to discontinue when they show signs of rolling in the suit, so that may only last you a short while. If you are in a pinch, I’d still give it a go. If your baby self soothes (thumb sucking etc) and just needs some help from not startling himself awake try the zipadee zip. They can still move their arms and legs and can roll in it, so you can use it even after they start rolling. Bonus points for both because they look totally ridiculous and adorable. The Merlin looks like a little space suit and the zipadee looks like a starfish 🥹 Best of luck to you!