Make some awesome Ultralight gear. Mostly I like their sleeping bags and insulated clothing. For many years I have used the UL Super Spiral Down Hugger #3 now called Down Hugger 800 #3 & available at Larry Adler Australia for A$329). Mine was 624 grams and rated -1C. Montbell have even improved this bag by moving to 1 oz more (and) of 900 fill power down. This is the Down Hugger 900 #2 at 690 grams and -5C, which is just awesome! This ‘spiral stretch’ construction means that they are the roomiest sleeping bags you have ever used. You can even cross your legs and sit up in them.
In Australia you will almost never encounter conditions where you will need a warmer bag than this. If you do (and as I do) you carry a down jacket and vest, you can put the jacket on and pull the vest over your lower body. This will provide at least another 5C worth of warmth.
Speaking of jackets and vests: I am particularly impressed by the warmth and lightness of their ‘Superior Down’ range. The coat weighs just over 200 grams and the vest a bit over 150. Their Clo (insulation) rating (eg measured here: https://backpackinglight.com/forums/topic/18950/) indicate that the two garments together should take you well below 0C. Think -10C. Larry Adler have them on sale at the moment for A$140 and $105 respectively, which is a bargain: https://www.larryadler.com/ Larry does not have the complete range. For that look here: http://www.montbell.us/ To purchase from the US you will need (eg) a Shipito account and a virtual US credit card – available from Shipito.
If it gets really cold I recommend a pair of Superior Down Pants at 239 grams.