Private car service recommendations from Rome to Siena with possible stop at winery along the way?

Hello all,
We are getting a bunch of things lined up for our trip to Italy in October. After 4 days in Rome, we are going to head up to Siena to stay at La Certosa di Maggiano for 2 days before heading up to Florence. We were initially planning on taking the train, but in my sleuthing we have figured out that it makes more sense to hire a driver, and perhaps even make a stop in Orvieto along the way. We would then likely hire the same company to take us to Florence after our respite in Siena.

So, does anyone have recommendations for some car companies that would do this? There are just 2 of us.