It looks like the 5e dragonborn does have dragon breath and also damage resistance of the matching type, but no flight. Also no natural armor, claws, bite, etc. Personally I would start with Sohleugir to get some of the physical traits that a draconic entity ought to have (even though dragonborn don't), maybe omit some things (maybe you don't need nictating membranes for example), and add the dragon breath and an appropriate elemental RR/DB bonus.