Kathi, I just wanted to post the same link, investinyourchest is a great blog.

Also, if you have the possibility to visit a Bravissimo store in the UK, they do a great bra fitting.
They also have a better sizing-range in UK-shops. I order all my bras online since I dicovered shops like Bravissimo or Figleaves (and my real bra size).

Straps that fall off your shoulders are an indication of a too big band-size.