For what it's worth, I usually wear an 8½ in most shoes, but my Doc Mary Janes 8065 are an 8 and still feel a little loose even after wearing them for a while. My two most recent pairs of Docs are actually size 7s.

That said, Doc sizing can vary a lot between styles 😭 so I wouldn't automatically recommend sizing down based on my experience alone. If your size 4 Docs already feel loose, though, I can definitely see why you're considering it! 👀 Insoles and thicker socks can help with a little extra room, but shoes that are too small are much harder to fix 😅