Hi there,
About the ride home – dont worry. Its not as bad as u think but make sure u avoid pot holes and speed bumps and that the driver takes their time. A good idea is to take a little pillow and prop it between u and the seatbelt.
As for sports bra – get a back size bigger than what you wear now. This ensures comfort against your incisions etc. Usually u should get a cup that is the size u plan to be after the op. However – I am currently wearin 2 cup sizes less than I am and I feel that instead of a big gap between my breasts – it holds them in nicely. (See *Sports bra post for full explanation.
Good luck!
xx