I'm another blind bat -6.5 and -7.5 in a contact lense prescription (yes, that's bad!). I still hold a Class 1 medical and an ATPL (in three countries at one stage).
I would strongly recommend the soft contact lenses as you get to keep your peripheal vision more easily (important with flying), and you can wear normal sunnies
If you go that way you should still carry a spare pair of glasses when you fly. I carry that plus spare contacts!
Good luck and don't be discouraged. I don't know about the RAAF though. I thought they still required 20/20 on entry but then don't care what happens afterwards (and a Hornet jock told me most guys end up wearing something before too long - especially after all the hard study slog!).