If you have time, this is an option. No idea what freight cost or time to Australia might be (six weeks on a ship?) or whether your stuff would get more or less banged up ... But worst case scenario in my mind is I am at the airport and cannot bring some essential piece of gear because of weight or size limitations. Not sure if the airline will always allow overweight/oversized just because you offer them money .... But I have seen people at the luggage check-in scale repacking multiple bags to try to get the weight low enough in all of them .... I am assuming that one was so heavy that even with overweight fee it couldn't fly.

Ship ahead ... or buy online and have stuff shipped to an address at your destination (hostel/tour leader/friend.) I have done that on a tour--mail-ordered gear I didn't want to pack (bike parts and tools for instance (and a case of Powerbars---very dense)) which I had shipped to a person associated with the tour.

On that tour several people did that .... and also several people did a gear run to pick up some readily available camping stuff at the departure city instead of packing and shipping it.