Does anyone have a recommendation on a convertible car seat that would be good for flying, and easy to install/uninstall in a rental car?

We have a Diono Radian RXT, but it's super heavy and not easy to install. I wouldn't want to bring it on a plane (especially if I'm traveling alone with LO) or try to install it in a small rental car!

I normally would just have LO fly as a lap child, but he threw a GIANT fit the last time we flew without a car seat. Hoping to avoid that again, especially now that he's mobile!

Any suggestions?