Long Term Rentals

The best way I have found to find accommodations in Germany and Austria is to use the town website (almost every town has one). In Italy it should be found at www dot town_name.it. Since your wife speaks Italian, she should have no problem navigating the website. Look for tourism, then accommodations. There should be a list of hotels, the Italian equivalent of a German Gasthaus, rooms, and apartments. I've found there to be two to three times as many properties on a town website as you will find on booking websites, that charge property owners 15% commission.

For long term rentals the websites most used by Italians are:
www.immobiliare.it
www.affitti.it
www.casaclick.it
www.idealista.it
www.casa.it
www.trovacasa.net
www.subito.it

Since presumably you are interested in furnished dwellings, the Italian word for “furnished” is ARREDATO or also AMMOBILIATO (although arredato is used more frequently).

For short term vacation rentals look into:
www.airbnb.com
www.casevacanze.it
www.wimdu.it
www.homeaway.com

Regarding which town to stay, It’s hard to respond to such a broad question.
I understand you don’t want big cities, but what size are you interested in?

If interested in smaller but still decent size look into the provincial capitals.
https://www.tuttitalia.it/capoluoghi/

If you want to get smaller, the choices are endless.

Also what are you looking for: hilltowns, seatowns, lake towns, Mountain towns?

I think the only issue is does the town have train access. My wife is also on oxygen so needs to be relatively flat. We love the Cinque Terre but is very hilly.

Under your situation, have you considered renting a car? My wife was in a wheelchair on our last trip, and the rental car got us where we needed to go promptly and efficiently. It certainly minimized the miles I had to push her chair.
Driving in Northern Italy and Tuscany is not at all difficult--other than crooked roads. You can see so much more with one.

didn't want to rent a car for a month

Padua may be a possibility, though it could be larger than you're looking for. I remember it as being relatively flat. It's on the main rail line between Milan and Venice and is well-positioned for visiting Verona, Vicenza, Ferrara and no doubt other worthwhile destinations. Padua has an attractive, good-sized historic district that I thought was excellent for strolling.

A larger city with even better rail links is Bologna, but it is probably too large for your wife.

Vicenza is a lovely, small city and in a great location to visit other places. I lived there for 2 years and loved it!

Treviso might also be worth a thought. Padua for a month as suggested above would also be great.
Verona maybe, but that is getting pretty big.

awesome suggestions
how about over in the Lucca area of Italy?

I have had a very good experience using the following for renting in Lucca. The site offers both long and short term rentals.

http://www.luccaholidayhomes.it