DH and i flew with DD at aged 16months to europe last year (total 22 hours plus flying plus stopover and transits etc) We left syd on a night flight, had bottles ready with water she could drink whilst taking off/landing plus dummy/and B.f whenever she wanted it, we took own snacks, like fruit sticks, heinz bars, cheese sticks (the ones not needed to be in fridge), tubs of fruit, as the airlines only had baby food with was pureed stuff which she never ate even when she was a baby. had a bag of mixed toys to rotate thru out the flight (mini doddle sketcher, finger puppets, new books, play phone etc) she was to a little too long for the bassinette but it gaves us some time where she wasnt in arms so we too could nap for short periods, and was at the maximum weight for it too but they let us use it. (u will prob have 2 make a request with airline for one)
we had her on our laps, DH and i took turns cos if u want a seat u have to pay the extra, there's a seatbelt extension u will need to use takeoff/landing & when seatbelt light on. u can take a pram to the gate where u depart (i guess it depends who u fly with) and they check it on under plane last thing and then bring it to u @ exit when u get off the plane, u might have to wait a few minutes for it at the arrival gate. wait til the last moment to get on plane, pack extra clothes - can get hot or cold on flight, layers good, extra nappies etc. we found DD took a while to get to sleep even tho our flight left at 9.30 pm and she would normally been asleep but then slept fairly well, even if we didnt, cos when she'd stirwe would wake to make sure she was safe in bassinette or change position in our arms. good luck. sorry for long reply, Hope this helps