Really want to see the Heart of Tuscany but without our own car. Where/How?

www.toursbylocals.com where I've hired private local guides in several destinations. You'll see lists of tours/itineraries along with the guide and the cost. I've found that if I want a deviation all I have to do is ask.

Edward,

I think you're under estimating the length of your time. The places you list will in reality take 8 hours.

Try http://www.toursbyroberto.com

Using his joinable tour (100€) or a private tour which he can customize for you.

I checked tours by locals and found this and this. It seems a little pricey and is a guide, but not a car.

It looks like there's Uber in Siena, maybe that could be an alternative. I hope you can find what you are looking for. I think it would be fun to drive the Tuscan countryside with someone from the area. If you just want to ride through the countryside, you could look into taking the bus to San Gimignano or Volterra.

When we stayed in Tuscany, we rented a car from Hertz at FCO Rome and returned it there. It was no more hassle than renting a car in the states. We did stay in an agriturismo in the countryside which is more convenient than having a car when staying in a town like Siena. There were some experiences, like attending Vespers and the Abbey of Monte Oliveto, which would have been almost impossible to do without a car.

Like I said earlier - if you want a deviation from what's written (a car) just ask. I found a guide in Barcelona and he single handedly ended up booking an entire bus for my group of 25! The guides are very good at what they do...even thinking outside the box.