Depends where you are going and how long for...
I travelled alone with DS when he was about 15 weeks old. We did 6 flights in 3 weeks & it was fine. He slept on our overnight flight to the UK. Did not sleep at all on the way home (8hr flight)
Take as little of your own stuff as possible. In hand luggage, take change of clothes (for both of you), nappies etc.
If you are bf, do that during take off & landing - it helps with their ears, apparently. If not, give a bottle/ dummy or whatever so your ds can suck.
Some planes don't have changing tables in the loos, so be prepared to improvise. That was the worst bit for me.
If you cosleep, you can do that in a hotel, if not, you can ask for a cot. I ended up cosleeping with DS when we travelled as it was comforting for both of us.
HTH