I'm in Scotland, but used to live in Cairns. At the moment the outside temperature is about -10.
The answer is merino wool.
You can buy this in thin base layers. For the temperatures you are quoting I'd use a set of thin leggings under a pair of MTB 3/4 trousers. A thin short sleeve T shirt style merino base layer under a long sleeve heavier weight merino top with a zip neck. To counter wind I'd use a Montane thin Pertex top which is breathable, fairly water resistant and cuts out the wind. Once you were moving and warm the heavier weight merino could go in the backpack. A pair of cheap but thick wool gloves will finish it off nicely.
I have had to spend a small fortune on warm clothes to find only to find the wonder fabric is wool.
One big advantage is you won't have to wash them every day to get rid of the stink.
(IceBreaker is my current favourite)