I'm going through this exact same debate. We are flying down for a Carribean cruise with our 8 yr old, 6 year old and 4 year old. They are all in boosters at home. I know we will have to use taxis several times during our trip. I'm thinking we will probably just bring boosters for the youngest two.
I know the last time we flew, we put two boosters in a black garbage back and checked them (SW Airlines). We also let our youngest ride in her carseat on the plane. Does anyone know if you can put their boosters on their seats in the plane?
Thanks for any advice input on this subject! (And thanks for the OP asking this questions!!)