Hi Anne!
I've had two fittings at Myer. One was outstanding I must say! The other.....
The lady fitted me for size and helped me with bra selection. She recommended certain styles over others for me to help give me the necessary support and lift required (I have sadly lost some fullness due to breastfeeding).
The other time, the assistant was rushed, wasn't particularly helpful (ie, you're a 12B, go find some bras and try them - no fitting assistance provided) and to be honest I left less than impressed.
I think if you can go to the store during a quiet time (ie weekday, not during lunch hour/after work) you will be more likely to get devoted attention than if you try to go during a busy time when the already thin on the ground sales staff will be distracted and less likely to be attentive. I'd also make sure I asked the staff for a fit specialist - as sometimes the staff on roster isn't actually trained.
Good luck!