One of the most wonderful places I've ever stayed was at Fattoria La Loggia, sort of midway between Florence and Siena. It's a working farm (they grow olives and grapes), and have 8 or 10 (maybe more) apartments that they rent, generally by the week.

The setting is splendid beyond belief in the Tuscan countryside, the apartments are both comfortable and gorgeous with wonderful furnishings and stone floors, and each day started with a breakfast basket delivered to the apartment with freshly baked breads, yogurt and fruit juice, coffee, and preserves made on the farm. The big decision each morning was whether to have breakfast inside, or put on a top and slacks and enjoy it on the patio outside.

Assuming it's still run by the same folks (I was there about 5 years ago, and Ivana ran the show), La Loggia is a perfect base for a Tuscan holiday.