I really like
Corinna and used to be such a stickler for the long e pronunciation because that was closer to the original pronunciation, but then I figured since I didn't care about pronouncing similar-sounding names such as
Callista,
Melissa,
Elissa, etc., with the long e sound, then why should
Corinna be any different? I think the IN pronunciation is more user friendly and either
Corinna or
Korinna should get you there if that's what you prefer as well. OTOH,
Corina or
Korina lean more towards the long e pronunciation.