Beverley.Rose,
If you look at old posts, you will see that I posted, at lengh, on bras for genetic men. I would estimate that you are an A cup at present and you should take your under bust measurement as a starting point for band size.
Finding the right bras, for you, is a very hit and miss afair, as is illustrated by my tale of 2 bras. I bought a pais of bras, 1 black and 1 white, but otherwise identital, or so I thought.
The black was fine, but the white was too big. Eventualy, I grew into it. One day, after a long day, wearing it, I developed a pain, in my left boob. 3 days ago I tried it again and the pain returned, within 2 to 3 hours. The souce of the pain seemed to be a seam, where the band joined the main part of the bra, about 1 1/2 ins., from the under wires, i.e under my armpit; yet the pain was concentrated just to the left of my nipple. When I took the bra off, you can imagine my shock, when I saw a bruise, at the site of the pain. I assume that the seam was causing a pressure on the lymph ducts, causing a build up of pressure. The black one remains fine and I am wearing it at present.
The moral is, however well a bra fits you, only a day's wear will reveal if it is comfortable