Hi there,
I would imagine that no matter the breast size you're beginning with, the pump will help you as long as you're using the right size cups. I am small to begin with, and after each pump, definitely get a bit of upper fullness. It doesn't always last, but that's because I am only a week in (started again a week ago after taking a 2 year break - life just got away). I did gain a bit of upper fullness that was permanent though, from my last time. I did not do it long enough to gain any proper growth though. In all honesty, I think this is just one of those "in it for the long run" things that is going to take time, dedication, etc. It is not the quick fix that we are used to getting in this day and age, lol! Just be willing to do it for the long haul, and there is no doubt that you will see change. I hope that helps put your mind at rest a bit