Perfect! This is the type of feedback that then let's me offer much more specific suggestions as to places you should look at.
First, take a look at
Borgo della Meliana that I had already suggested above - while they are an estate, they have a completely separate house with its own garden and pool away from all of the other lodgings so you would have complete privacy.
You should also consider
Villa il Poggiale - the main villa has rooms and suites, but they have what they call a "depandance" 200 meters from the main willa which is a separate house which would offer complete privacy. Own kitchen and lots of space for you, but then you'd have the hotel's wellness center, restaurant and pool available as well.
Staying in the area between Florence and Siena, not as luxurious but definitely comfortable would be the house
Le Sante Marie. While the house is divided into two smaller apartments perfect for couples, you could also just get both apartments to get complete privacy having the entire house to yourselves.
As far as entire villas and farmhouses, they tend to be large as in for groups of up to 20 people... that is why I've been recommending estates that have the main villa with another smaller house nearby. Cost will obviously be different when you consider a place is for 2 people as opposed to 15 or 20 people, but if you want to look into these options, you can check them out and see whether the extra cost is still within your budget.
So staying in the same area, the smallest villa that comes to mind is
Villa Corsanello which is for 8 people and is to the south of Siena, in the magnificent setting of the Crete Senesi. Then there is the
Villa La Medicea to the south of Florence in Chianti so also beautiful surroundings. This also has been divided into 2 apartments but you can rent the entire villa easily.
A bit bigger but definitely still within manageable size would be
Villa Vianci near Monteriggioni.
Take a look at them all and contact them - those pages have direct websites and forms to the owners. Find out cost and availability, and that should give you the opportunity to better evaluate your choices. All of them are beautiful and in stupendous settings in Tuscany, so choice has to depend on factors that are up to you and your husband.
Need more suggestions? Do let me know which ones you like more or less so that can help me get more ideas of what you like. ;-)