Welcome CaseyM!
I am not sure what suggest on the ob front as I am not in Perth. With obs in general I find asking friends and family is a good way to find some one who people have been happy with. Of course HG isn't something that people really know enough about to know if a specific ob is understanding of it or not, so I'm not sure if word or mouth is helpful this time. You could always try posting a thread in the section for WA members?
Do you you have a good GP who will help you out with treatment and/or referrals to obs they think will help you? If you don't that might be the first step.