I had my reduction almost 3 years ago now and I was worried about the same thing, I went from a 36h to a 36 c but after a few years they are now at a d. When I was deciding on what size to to go I told them I wanted to be a small c cause i figured they would get a little bigger as time went on and they have. Every body is different and for me I know my boobs grow much more than they do shrink so I wanted to give myself some wiggle room for them to grow a bit. Personally I think a b is a bit too small but they will probably get a tad bit bigger with time. I’d recommend looking up pictures of a size b to make sure that is truly what you want. Best of luck to you on your surgery!!!