I would not buy the extra seat. We have tended to fly WN because you get a free middle seat for the little one (as long as the flight is not sold out). We brought a car seat on WN on a few of our more empty flights and it was always miserable. Lugging the seat around the airport, through security, buckling it in, etc are all something else to keep your hands full (while you already have the baby and their stuff in your hands). Then , when you are on the plane, the baby is just sitting there crying at you because you are not holding them. Definitely not worth it for our kids. I have had my up-to 1 year 11mo old (3 kids total) on my lap for flights to Europe and Hawaii and it was fine.... though I suppose every child is different.