5 day road trip in Tuscany... Are there any hidden gems?

Ciao a tutti! My wife and I are traveling to Italy in early May and we are giving the finishing touches to the itinerary.

We are from Argentina, I speak some italian so I dont need english tours, we also don't like much crowds and overly turístic destinations (nor overly expensive)

We are spending 4 days in rome and 2 in florence. Then, we are renting a car that we must return it 8 days later in Mapensa Airport in Milán.

We wanted to do 3/4 nights in Tuscany and 1/2 Somewhere mid way to Milan... What are your suggestions of places to visit or stay that perhaps fly under the radar for most tourists?