We flew to Sydney (from Perth) with our DS at exactly the same age. I - like you, was very anxious. We also had Daylight Savings to contend with!! We basically just flew by the seat of our pants (pardon the pun) on the way there with no problems. I was breastfeeding at the time, but don't like to get my boobs out in public, so he was happy to have a bottle of formula at take off. One trick that we did learn for keeping the bottle warm for 4-hourly feeds - boil the kettle before you leave home, if you have an insulated bottle carrier (keeps warm or cold) it's just right at feed time ie 4 hours later.
But I agree woth previous post - if you're flying Qantas, ask for the "bulkhead" seats. These are the first row (after Business Class damn it) and have little cots that attach to the wall - very handy! I'm pretty sure that Virgin is "get what your given", but call them re: bulkheads anyway.
But... on the way back, DS had a head cold - we reluctantly gave him Demazin to dry up his nose and he slept the whole way home (bad parents I know)!
Hope it helps!
Kerry, WA, DD 09/00 & DS 11/05