Archosaurs. Not lizards. Archosaurs - crocodiles, dinosaurs, and birds. Archosaurs are mostly warm-blooded in every sense of the word (and run hotter than mammals), have families with both parents involved in care for the babies (unlike mammals), and some are as intelligent as apes. A creature doesn't need to be a mammal to be warmblooded, intelligent, and social. Parrots do it. And they do all that without any hint of a boob. Some have no visible (to humans) differences between males and females at all!
And no, I'm not advocating that dragonborn go that far. I'm okay with dragonborn males being larger and stronger than females, although it is disappointingly uncreative. I can even live with them walking on their feet instead of their toes. Just...get rid of the human (not mammal, human) genitals, please.