Down South is more of a summer time trip. December to March around Denmark, Albany, Mt Barker & Porongurup Nat park, Stirling Ranges, etc is just choice-bro. Although a lot of it is not much different from country-victoria.
Winter time is ball freezing cold, although from Victoria you might just feel right at home.

For winter time in the west you really should hire a campervan and head up north. Anywhere north of Geraldton is good. Exmouth to Broome is great.

Karijini and the Hamersleys are great

and all different to Victoria.