Palazzo Belefiore looks promising. http://www.residencebelfiore.it/
Looks like we would need to rent two apartments for about $3000 total for the week.
Clarissa, with its frescoes looks particularly interesting. Pictures also at:
Orsanmichele looks like it might be perfect. I haven't yet checked price, but it looks
like it is available the week we want.
The frescoed ceilings in this one look very nice...$3380 for the week. Don't know if it's available.
What looks to be the same one is listed at $3076 here (but maybe that's low season)
This one is fun just to look at (not available):
There are a bunch together in this building:
This one is sort of cool as well, sort of strangely furnished, though...no prices given:
If we wanted to go truly high end, there is a villa available for $9750 (holds 10 people).