We have a doona. Best thing we've ever bought. If you are reading this, and see recommendations for other car seats, done just chuck the Doona in the mix.
It is not a standard travel system.
There is no clip on chassis
No putting wheels on and putting it up in a car park.
Literally, park, remove car seat, press magic button and it transforms into a pushchair. It's amazing.
And yes travel systems can seem convenient, but from seeing us park up in a parent and baby space, next to people half way through sorting their travel system, we are still ready first.
It fits down train (and shop) aisles, easy to sketch on a plane, and it means you have your boot free. Putting it down on a bus means simply pressing a button.
All hail the mighty doona. It is the answer to your problems.
You might tell, I love the doona.