Agreturismo or no?

Many agriturismo accommodations require a minimum stay of one week, but many do not, so that option could be available. Just be aware that agriturismo are basically abandoned farmhouses that have been restored, refurbished and reconverted into vacation villas (some are sort of working farms so that they can benefit from some government incentives and subsidies), as a result they tend to be located in secluded rural locations which require a car to reach, so be ready to rent a car.

The article below lists the best websites to search for that type of accommodations. The article is in Italian, but all you need is to click on the websites they mention, then click on “accedi al sito” (Access the website).
https://www.freeonline.org/migliori/migliori-siti-per-la-ricerca-di-Agriturismi.html

We stayed at an agriturismo in Pienza called Fonte Bertusi and loved it. I think we were there for four or five nights. From there we did Montepulciano, Montalcino and wineries, cheese farm, etc. They served breakfast and had a pool. You had an apartment where you could cook if you wanted to. I would return in a heartbeat. We got to know the owners on a personal level and they had a huge notebook of suggestions and places to go. They were able to book many things for us we wanted to do. I would recommend staying at one. The scenery was beautiful.

I don't remember any requirements for a minimum stay as mentioned by someone earlier. I've stayed at a couple for 2 or 3 days. I found them very charming and very B&B'ish in Tuscany. I think it is a great option!

I recommend you check the websites in the article I mentioned.
Yes, some do have a minimum stay requirement, but there are also many options for very short stays.