pinniped

Perhaps a bit OT, but I've had good luck with Booking.com in Italy to get some nice apartments in a few places.

I wouldn't do Airbnb on any stay where I wasn't prepared to find an alternative at the last minute for whatever reason. (Owner flaking, it being an outright scam, apartment being disgusting or otherwise not as advertised, etc.) Booking.com's property listers tend to be more professional management companies - at least at the places we've booked.

Another option for Italy with Marriott points is to accept a Courtyard or similar outside of a city center. Then finding a new-build property with 2 doubles is probably more do-able. Trade-off is a lot more daily time on a bus/Uber/train/etc. to get to the places you really want to see.