Icebreaker midweight apex mens jumper for $89.95 at Mountain Designs
Icebreaker is really something you want to get on sale. At $179 its a relatively expensive buy while at $89 I reckon its a bargain. 50% off. This weight is pretty much perfect for most Oz weather either on its own on the mild nights or as a sub layer under a light jacket when the seabreeze is steaming in.
I normally take a small / medium in most of my clothing. Icebreaker sizing tends to be on the small size torso wise so you can easily live with a large if your a comfortable medium.