Mark,
you made an irrelevant connection between width and "height" of a wheel.
width on a 18" wheel can be exactly the same as a 19" (I assume you keep the tyre profile to be within oem specs to avoid errors in speed reading)
also need to bear in mind the offset of the specific model you are getting in order to clear the Brembos.
I voted 9.5F and 10.5R, but they'll be heavier than the other option, mind you in getting 19" you might as well go the whole hog