2 door car and convertible seat question

shoebox4

Does anyone know what convertible car seat fits in a 2 door car? I have an Infiniti g35 coupe which does not handle car seat very well unfortunately (I know I should change my car but I dont want another car payment, so I'm going to hang on to this car until the wheels falls off). The Graco Snugfit barely fits into the backseat of my car, but it does work. I'm wondering what convertible car seat will fit into my car next?

DH drives an SUV and we're getting a Britax into his car. His car will be used mainly as our family car and my car will just be an emergency car but I would still like to have a car seat in there for my LO.

Thanks!