Oh yeah, if you are a DD already, don't bother with Bras n Things, Kmart ,etc...you will need a specialist bra fitter.

Not sure where you are, but there is a good one at the the Junction in Camberwell - they lots of old lady knickers and swimmers, but they are fabulous at fitting, and since they aren't perky little 18 year olds with B cups, they don't look at you like a freak
Also a FABULOUS store that specialises in D+ bras, Brava, in High St, Malvern or Prahran.

If you aren't in Melbourne, I am useless pmsl