For a luxury experience I think of a spa or resort in a beautiful seaside or lakeside location, not a big city. Places like Lago di Garda, Bellagio on Lago di Como, or maybe Puglia. Lots of history there, especially in Lecce, the Baroque city nicknamed the “Florence of the South”. And beautiful seaside towns like Monopoli and Polignano al Mare.
You can see photos in travel blogs such as this:
https://www.asmallworld.com/explorer/articles/the-most-beautiful-places-to-visit-in-puglia
Puglia is known not just for the coast but for the beautiful inland area, dotted with special inns known as masserie. some of them are simple farmstays, but others are 5-star resorts offering a luxury experience, such as this one:
https://www.masseriasandomenico.com/en/
To reach Puglia, you can fly into Bari or Brindisi, or fly into Rome, spend a little time there, and take the train directly to Bari. The coastal towns I mentioned above, as well as Lecce, can be reached by train. But for the interior (Val d’Itria) and masserie it is best to have a car.