I went with my mom on a south Italy tour group to Rome, Vieste, Matera, Maiori, Amalfi, Sorrento, and Naples a few years ago. Felt weird being the youngest and surrounded by boomers, and I can't say I liked having to follow around the guide with people wearing tacky earbuds. But the arrangements were worthwhile, and they let us loose a good deal. My mom wants to go back this October for a week in just Rome, to see the canonization, no tour. Gonna wish I could revisit Vieste, or check out any of the places mentioned by OP, but experiencing the city again in weather that hopefully won't be as sweltering sounds nice.