With a seat back that kind of slips into the base - very nice for traveling! The back is adjustable to different heights, and has a slot for the shoulder seat belt to slide into so you get a very good fit to the child. There are several models (it's been a few years, but I think ours is a "Roadster" model). We took one of these along when we flew - very easy to stick in a duffel, or even a plastic bag at the airport and check. Only downside is the price - > $100 as I recall. But worth is as it's a VERY SAFE seat, comfortable for kids, and with the multiple adjustments to the back, will fit a child for many years! Am sure you can find them on the web, sorry don't know who carries them anymore as my DS is 9 now, so it's been a few years.....
Good luck!