Check but I think that WA also has a restriction on rim width, that being 7". So a staggered fitment such as 7"/8" would be a no-no.
I'd agree that 16" dia rim would be ideal (I've been looking at the same), but I think you'll find that there's hardly anything in that size available in Australia; it generally comes down to a choice between 15" and 17" (or bigger).
Check with the authorities as to what is permitted, and also your insurance company will want to know (and approve, or not) what non-factory items are fitted to your car.
Merry Xmas and good hunting.