So, taking Angie's advice to me from the other day, I'm looking at my bras. Sometime this week I'll go get a fitting, just for some professional advice, but in the meantime perhaps someone can tell me what my main problem indicates:
My bras all seem to fit ok when I put them on (no gapping, poking, or bulging) and the back and straps generally stay in place. However, the front tends to slide down by a couple of inches in the course of the day, and the "girls" end up hanging flat against my chest, squished down by the bra rather than being supported inside it.
I've tried bras in bigger and smaller cup sizes and I end up with either gapping or bulging, so I don't know if that is the answer. Maybe it's just a question of shape?