shelter - sleeping bag
With a decent sleeping mat you’re not going to get cold from laying on the ground but the night time air temperature makes a big difference. Australia is a huge continent and there’s a big difference between what’s needed in Tassie in autumn and Darwin at the same time.
The south of Australia is temperate: hot days and cool nights in summer, cool days and cold nights in winter. Not deep snow, blizzard cold, but light, frosty cold.
A 0ºC bag, (32ºF), should be adequate for most nights in Australia. If you are at altitude, or hit a cold snap, bung on a few woollen layers, or throw your jacket over the top.
Head up north and you are in the tropics. In winter it’s a Dry Season paradise with warm/hot days and warm nights. You don’t need to get into a sleeping bag when the minimum overnight temperature is 22ºC at 5am. Maybe a sleeping sheet is all that is required. But inland in the tropics the temperature can drop overnight, particularly at altitude. In summer, the Wet Season, well, pick another destination.
Let’s get contentious: feathers or synthetic?
Feathers are compact and warm. Problems are cleaning and what happens if you get it wet. To generalise and oversimplify, feathers are better in the cooler and inland areas.
Synthetics are more bulky for the same warmth but are easy to wash and just as warm when wet. Synthetics are more suited to the warm and humid tropics and coastal areas where you can get away with a thinner bag.
You choose depending on your itinerary but in any case get a decent silk liner sheet. Much easier to wash that regularly than the bag itself.
Remember it’s a bitch to be cold night after night.