Hi there! Both my kids were swaddled until about 5 months. I guess I'm not sure if what you'd prefer to do at this point is teach your baby to sleep without being swaddled, or just find a way to keep him from unswaddling himself.
If you want to continue swaddling, what we did when our son was breaking out but wasn't ready to give it up, was similar to the miracle blanket concept. We folded a receiving blanket in half so it made a triangle and put it underneath him so the long side of the triangle was at armpit level. Then we tucked one corner over his right arm and underneath the right side of his body, then did the same with the left side. With his arms tucked tightly, we then used the Swaddle Me blanket (has velcro) on top of that, and it kept him from getting out. It also kept him warm in the winter.
My daughter transitioned out of it by tummy sleeping (as others have said, once they're able to roll on their own, it is safe to let them tummy sleep, safer in fact than giving him a blanket at this age). It was actually a two-fer: she took care of the paci problem by learning to suck her fingers. With my second, he hadn't learned to roll over yet but we were in Dallas in April and it was way too hot to keep swaddling! We weaned him off it by swaddling with one arm out, which he got used to, and then the other. I admit that there was a bit of crying involved because he was learning something new, but he also learned to soothe himself by sucking his fingers.
Best of luck!