I'm just back from my annual Sydney visit. I wear light, loose leggings which are comfortable for sitting in for hours, with layers : strappy top under long sleeved top and thin jumper over. The bra is usually first to go! Tends to dig in after sitting squashed in a seat for a few hours! I have a big pashmina/wrap which is useful at this end in lieu of a coat and can be used as a supplementary pillow or blanket on the flight. I take a spare set of clothes in the hand luggage just in case the suitcase goes AWOL but rarely change on the flight. I wear easy to get on/off shoes, take them off on the flight and replace with thongs (flipflops) for loo visits and for use in transit. I just take wipes, toothbrush/paste, small deodorant, mini hand & face cream, medication and hairbrush. Remember most transit airports have aircon and can be quite cool. Less is more when travelling. I always take far too much stuff......
Have an amazing trip!