My current shoe size is 9.5 extra wide Asics, for context. I tried to go to a 9 for shoes but they were painfully tight. My whole life I've worn 9.5 or 10 most of the time.
So the large boot might be a touch roomy for you since it sounds like I'm a full shoe size above you, but can always order some from Amazon to try and return (which is what I had to do a few times). I feel like the shoe size conversions on dive booties are kind of all over the place, you really just have to try them on. For you, either large or medium should fit with this boot.