One of my best investments in life was going to a boutique bra store, getting a fitting, and purchasing a bra from France. The salespeople measure you topless, which was kind of weird. Then they get 8-10 bras and have you try them on, and then they evaluate them. Turns out, they know bras. They acutally know what they are doing. I bought a bra which is more comfortable than anyother bra- ever. Works under T-Shirts, is pretty, and is comfortable. They have kept my information on "file" so I can have my husband buy me properly fitting bras in the future.
It is expensive, but like buying good shoes- so worth it!
Anyhow...it would be a solution for you to be able to customize your bra, so that the cup was slightly tighter on the one side. 