Yes, please make them normal pet-sized animals. If you want your character to still have them (instead of say the pokemon being temporarily shifted into a squirrel that wanders the university grounds) keep in mind they need to be pets that could conceivably live in student housing. (Or if your character is faculty, you do have a bit more leeway.)

For the sake of simplicity, let's leave them as non-sentient animals rather than human NPCs. Thank you!