Where is Naples?? If you want the best pizza that city is mandatory, and I'm saying it as a northerner.
Next I'd go with: Rome, Florence, Venice and Bologna. Somewhat smaller / less touristy like Verona (generally known for being Romeo's and Juliet city) may be nice too.
I live in Venice and it's a damn clusterf*ck rn; worth seeing it at least once, sure, but I'd avoid it in this period. Heck, maybe I'd even visit it in winter/fall/spring if I were you, I'll never get why tourists seem to want to see it in summer when it's a hot humid crowded hell.