yep! baby rats. He's probably big enough to eat fuzzy rats (babies with fur - some have eyes open, some have eyes closed). A fuzzy rat in the 20-30g range is perfect for a 220g snake. Most don't have an issue switching to rats if you start them early enough. I've got some that switched immediately. They saw dinner and didn't care if it was a mouse or a rat. I have another who took a little bit of convincing to switch to rats, but now I don't have any issues with her.
Switching to rats will have headache in the future because you won't need to feed 4 mice at a time. You would only need to feed 1 rat. Now, your snake can still grow and thrive on mice, it's just you'll have to feed multiple prey in one sitting or offer frequent meals.
Once you feed him hopper mice for a week or two, then feed him an adult mouse, then the next week feed him a rat fuzzy and see if he takes it. If he does, then don't give him mice ever again! If he doesn't eat it, ask for some used mouse bedding and let the fuzzy roll around in it. Then offer and see if he'll take it.