Wow, Susan, congratulations! Maybe Rosie will feel "motherly" right away this time round, and Sophie isn't accustomed to being an "only child" anyway, so the introductions might be smoother this time.
I know several people disagreed when I advised getting a boy, rather than another girl, but I really do think it makes a difference, despite my experiences with Jamie rejecting any gender. One very experienced shelter worker explained it this way: Male cats have larger territories than females do, and their territories encompass those of several female cats, so they're less likely to act aggressively when encountering other cats. Females have much smaller territories, and usually only tolerate related females in them, but accept "incursions" by males.
My sister isn't happy unless she has at least three cats, and has often remarked that it's much easier to introduce kittens of either gender into a clowder of castrated adult males, but a (spayed) adult female will often be very unhappy or try to "rehome" herself if a female kitten is brought in.