I'm travelling to Spain in February to visit my mum (what is it with parents and moving to bloody Spain?!) with my 2.5yo - at 34wks pregnant. Shame we can't go together and help each other out 
I highly recommend buying a portable DVD player and loading up with peppa pig or whatever keeps your toddler occupied for five minutes we paid about 40 quid for ours and it was worth every penny. Are you taking the car seat with you for the baby? Could try alternating children on your lap that way? Or get a fabric chair seat thing - I've got a Phil and teds one which you can attach to yourself as well so keep your hands free.
Any reason you don't want to take your double buggy? I'm sure someone would help fold it at the plane, then you get it from baggage claim at the other end. If not, you can get cheap doubles second hand often I find.
Have a bag of small cheap toys, wrapped if your toddler loves unwrapping as much as mine does, and bring these out periodically. I packed six last time for there and back. Sticker books, magnetic games, felt pictures, reading the inflight magazine and repeatedly throwing it on the floor for mummy to fetch are all good. Ooh, and food/snacks. Lots.
Tell you what, shall I report back after my refreshing hellish trip?!
Ps. What am I supposed to do with the toddler when I need the loo every 5mins ??! I'll barely fit in those loos, let alone with him!