T is 9 months and we are retiring her infant car seat in my car and putting in the convertible car seat- which was previously our backup when we used one of our other cars. I am now shopping for a lightweight carseat for the few times a month she does not ride in my car and for the 3 flights we are taking next year that will be easy to quickly install in a cab- I would love for it to last us at least until she is 2. Right now she weighs 17 lbs. I would double love something that ships via Amazon Prime. Any recommendations?