[2nd Edit: Apparently the kitchen is available--here's a quote from Tripadvisor: "Kitchen and fridge at your disposal." We did not use them.]
We really liked this place last May: Antica Sosta, Via Dante Alighieri 145, 532027, San Quirico d'Orcia. It is not in a town you mention, but is quite close to Montalcino and Pienza etc., and about 1/2 hour to Montepulciano. We stayed in an apartment with one double bed, but there are other apartments in the building. The lady who runs the place is really nice, and provides a nearly unbelievable breakfast plus 24-hour access to cakes and other pastries for snacks.
San Quirico d'Orcia itself is delightful, with medieval streets and buildings, wine shops, and a cafe in a tiny square next to the church; also, there were almost no other English-speaking tourists when we were there. There is a wonderful restaurant in San Quirico--on the right about a 10/12-minute walk into town from the Airbnb. I don't remember the name unfortunately, but it is the one with the nice shaded patio in back. It was so good that in multiple visits I never got past the first thing on the menu, pasta alla pomodoro, which I had with Tuscan bean soup. Finally, SQ is pretty level, so the walking is easier there than in the hill towns.
We thought this whole area was fantastic. Just drive in any direction and you come to one amazing town or view after another. Sant'Antimo Abbey is also wonderful, and pretty close by, though we would never have found it without the GPS. BTW there is a lot of hiking too, even to Pienza (!), though we did not try that.
