Whatever fits and you can get a decent price on. Check out Liquid Elements in Bentley if are close by. It's got a 6" spread so you've got your choice of any boot on the market.
I got some Ronix Ones off Amazon and then went through a USA forwarding company to get them sent through to Australia. Got them for 1/2 price and within a week. Flick us through an email if you want more info on what to do.
ronix ones are super comfy
Www.shipto.com are the guys that allow you to ship to a USA address and forward it on. They charge you $8 when you register but it's credited to the first shipping you do.