Omg Stephhhh! V glad to have you back <333

I have far too many characters, but some options...

Theodore Gallivan was his dormmate in Ravenclaw! I can't remember if we ever established anything with them back at Hogwarts but I could see them being friendly?

Ari Fisk is in Potion and Plant Poisoning (at Hogsmeade hospital), probably thinks Harry should TAKE BETTER CARE OF HIMSELF and stop drinking experimental solutions, please.

Rosamund Bones is a fairly nerdy healer and was a Gryffindor in the year below him!

Ewart Fraser is Idunn's eccentric father, also into experiments of a kind.

Savino Zabini is a foreigner and a Seer and is also privately aware he is dying, and could probably be tempted into signing up for some experimental test subjecting for interesting potions because ~yolo, it can't make things any worse?

James Fletcher doesn't have any weird problems of his own but would probably still sign up to try some weird shit for cash during the summers. Or for free, actually. For the bragging rights. xD