Nicole 4138, welcome to Airbnb hosting.
Climate varies across Australia, and while winters in NSW can be mild, Perth tends to be colder and wetter.
In our 2-bedroom cottage, we opted for a split system air conditioner for year-round use. Most guests turn it off when they go out, but I plan to install a motion-sensing thermostat this year.
However, we do have lined curtains and blinds and remind our guests and remind guests about them during check-in. We also provide extra blankets and a thicker quilt in winter for added comfort.