Carseat in airport

How old is your DS? We have never used our car seat on board, and have checked it in instead. But I personally think it would be a PITA if you have a toddler. And if you have a baby, a bassinette may work better for you. You just have to ask when you're checking in for one.

The problem I experienced with the bassinet was that DS was only 7 months but crawling, and that meant I couldn't really have him in the bassinet unless he was fully asleep. As soon as he woke he would try to get out of it, so that meant I couldn't really get any sleep in case he woke up (but then I was travelling alone with him). Your DS may well be too big for the bassinet and I don't think they confirm the actual booking of them anyway until you check in, giving preference to younger babies on a first come first served basis. I guess that may vary from airline to airline. I think your getting him his own seat with the carseat is by far the better way to go. However the pain in the butt part would be having to carry it and having no trolley once you go through departures.

I found the bassinet really useful for stashing stuff in during the flight. Not much good for anything else though

I used a carseat with my two year old to travel and it was an absolute God send. Even all the attendants on the plane came to us throughout the flight and said what a fantastic idea to put him in his carseat and how lovely it had made the flight for him.
Carrying the carseat around the airport it a pain but worth it. What we did was keep our buggy till we got to the gate and then put the hood of the buggy out and rested the carseat on top of the hood. You had to be careful but it worked. Of course when DS wasn't in the buggy we sat it in the seat of the buggy.
If there are two of you traveling then it shouldn't be too hard to manage.