Hiya Babymolly - I flew to Aussie and back on my own with my DD when she was four months old. I had been told to feed her (bottle or breast) on take off and on landing, and if she not hungry give her a dummy instead. It keeps their mouths sucking and is the best thing to ensure their ears don't get all blocked up.
I thought Elsie would sleep once the plane reached altitude but she didn't! So I just talked and read to her and let her stand up on me to see other passengers for the whole flight, it was tiring for me but she loved it and actually we had a good time!
Also the flight attendants are really happy to sit with bubs while you have to go pee or something as well!! Oh and the change tables in the toilet are tiny, and you can guarantee that your bub will do a giant poo that needs to be changed before the other passengers complain about the stink!!!!!!!
Hope I have been of some help, lol! Have a great trip.