A.B.
I flew a lot with both of my kids from the time that the oldest was 2 weeks old.
It sounds like you've flown with him before, so I'll assume that you're familiar with having him either nursing or taking a bottle during take-off/landing to make sure that he doesn't have pressurization issues.
If he sleeps well in the Moby wrap, put him in it in the airport and try to get him to sleep before you board, then just continue to "wear" him during the flight. You can also bring a full size pillow and small blanket, and lay him on the pillow on top of your lap. I always found that the steady hum of the engines and dim lights during night travel put my kids right to sleep, so I always tried to travel at night to make it easier. Bring his favorite stuffed animal, bedtime books, etc. so that he has something familiar to him at bedtime.
Another option would be to gate-check his car seat so that you have it handy, and then shortly before boarding, ask if there are any open seats. If there are, they might be willing to switch your seats next to an open seat and allow you to put his car seat in the open seat.
If you haven't had seats assigned yet, try to get the window and aisle seats in one row. A person traveling alone will be less likely to book a middle seat, and you have a better chance of getting the whole row than if you book a middle & window or a middle & aisle. If someone else does end up in the middle, they'll switch with one of you happily. Or, they might be willing to try to switch to another open seat if there is one.
Good Luck!