Check out the mifold chair for kids it’s great for when you have to use taxis or a rental car https://www.mifold.com/ it just simplified travel so much for us.
We have a mifold for the older kid, but the younger one still needs a full carseat. When they were infants it was easier because I could strap them into the seat before the car arrived, and then just quickly buckle the seat in. But in the 11mo-3 year range, I need a full carseat that has to be installed before I can strap anyone in. :(
