There is? In a tabletop game the words "my character is a female" are not enough?
I don't think there's much point to putting breasts on dragonborn unless you are trying to sexualize them for human viewing - making it basically a question of marketing, and the artwork you'll be using to help sell the game to real-world humans, rather than one of fantasy biology.
For me, putting breasts on something that is more reptilian than mammalian is likely to come across as jarring, and a deliberate attempt to use sex to sell me the book. Vaguely insulting, even.