I think that's the way I'd go as well. The transmutation ability at, I think, 2nd level is right up Snape's ally. And then you can choose some abjuration spells like Shield and Absorb Elements, and some Evocation spells like magic missile and fireball.Potter magic doesn't quite fit D&D's schema, I would say the Transmutation subclass, with a dash of Abjuration and Evocation.