I have the exact same problem as you, and I've had the same experience with Victoria's Secret. My straps always fall, and they did the fitting, and my straps still fall.

I haven't really found a solution. I adjust myself in public a lot!

At home my solution is no bra. I'm not quite the same as you-- I'm a little bit on the small side. Small enough that I can go for a jog without a bra. I can almost get by (socially acceptably) without a bra at all, but I'm not quite rebel enough to do it. I feel unprofessional in the workplace.

I guess part of my definition of "professional" is "wears a bra"!