Another fan of going to a specialist shop and getting measured. My local shop were incredible. I was wearing totally the wrong size and had bra 'squelch' front back and sides along with a droop. She didn't even measure me, just took a look at me in my old bra, asked the size of it and handing me a bra. I could not believe the difference. I ohhhed and ahhhed so much that the lady in the next changing room said, 'Can I try on the bra that lady is trying please.'
She even showed me how to put it on properly i.e. lean forward and then when it's on 'lift' your bosoms up in the cup. I went in feeling a frump and came out feeling younger and slimmer.
I'd been afraid that the bra she chose for me would be much more expensive than my M&S usual, but it wasn't. I bought two bras and the matching pants. The bra is a Charnos Rosalind...but I guess everyone suits a different bra. It washes very well too.