I've done lots of flying Perth-Melb with bub, from a few months old. Try to get a bassinet but keep in mind they may not like being put down in it! Having a spare seat next to you is also wonderful in lieu of a bassinet IF you can get it- try to check in early and plead with the check in staff. If you have pillows (provided on board) and baby's own blanket/swaddle/bunnyrug and a toy or something familiar from their own bed you can lie them down on the spare seat for periods to give both of you some space to stretch out a little.

Other than that have dummies, burp clothes, wipes etc easily accessible (ideally in a small separate bag at your feet) so you don't have to try and pull things down from overhead compartments with one hand, with a wriggly or upset baby in the other.

I breastfed DD at take off and descending when young, it calmed her. I don't know how much choice you will get with booking flights but where I could I also tried to book flights that coincided with nap times so that DD would sleep through part of the flight.