I have a 21 month old DD and need to buy a car seat that will stay in place with just a seatbelt (to use on an airplane. At the m she has a fantastic seat that i brought back from Aus but like all Aussie seats it anchors into the boot of the car as well as the seat belt points, so it isnt secure enough with just the seat belt. As she will have her own seat on the plane next trip im forward planning to get her a seat that anchors with just the seat belt? I was thinking that as she weighs 15kg's already and she is tall that id try to get a next step seat? her current seat will be fine for now and hopefully as main seat for the next 12 months. So the new one will be a spare for baby sitters and the journey (i realise it will be illegal in cars in Aus, have a spare there that will bolt into car boots!)so ive seen this britax trio that says it goes from 9 months to 11 years? anyone gt one, seen one... decided not to or to buy one??? any other model suggestions?