All 3-series BMWs are the same size. The next size up is the 5-series, and they're liable to be too big for you. Also, I don't think that they come as coupes.

Speaking of which, I don't really understand why you're so opposed to 4 doors. Is it that the styling isn't sporty enough or that you think those two extra hinges somehow compromise the car's performance? Actually, you can get a G35 sedan (the "sport" package) that has more power than the G35 coupe.