Try John Lewis they have a display to show you how it all works, as they can be fiddly to put in, the 360 is great for getting a small baby in your car. It's when they get bigger...
We are the now "proud" owners of x4 sizes of Baby /Child seats. As they grown you have to change them to fit the growing child. Thank goodness the Isofix base fits all sizes as they are not cheap.
I have now got GC's aging from 12 months to 8years, car seats are in and out of our cars all the time.
You also can get "booster" seats which are direct isofix so we now have x2 of them in our collection , they are much easier to set up and store.