If you've stayed at Fattoria Tregole, please let me know how you liked it. If you have suggestions for other nice B&Bs in Tuscany which don't require a 1 week stay, I'd also like to hear about those.
Tom - Having travelled my Italy for many years I would suggest -
http://www.casolarelibbiano.it/
Just outside of San Gimignano and very close to Siena as well as Volterra. Have stayed there many times and love the place and the proximity to the area in general.
Ciao, Greg