Smaller town to base in near Florence

Have you been to Siena? I spent five nights there, and loved it a lot.

If you stay in Siena, you can take day trips to Florence (1h 15m by direct bus), Montepulciano (1h 15m by direct train) and San Gimignano (1h by direct bus). Siena is a wonderful place at night after the tourists leave.

I used Montecatini Terme as a base. Small, walkable spa town on the rail line between Florence and Pisa. Bonus: funicular to Montecatini Alto. The spas have a Belle Epoch feel and may offer entertainment during the day. Also famous for mud baths.

Take a look at Fiesole.

Arezzo is quite nice. Less touristy than Lucca or Siena. Fiesole is super close by bus.

How small, and how far from Florence? And what else do you intend to visit from there besides Florence. There are lots of choices.

Pistoia is a nice small city and very welcoming to tourists, but not overrun. It has notable historic and artistic sites and a convenient train station. It was the Italian Capital of Culture in 2017. https://www.italiani.it/en/Pistoia-Italian-Capital-of-Culture-2017/?cn-reloaded=1

First thought is Siena. Smaller, but not so small that your grandson will be bored to tears. Arezzo would be another choice along those lines.

Thanks for all your replies. I am going to have to give it some thought. Was leaning towards Lucca because of the wall city and I know the teenager would love the biking. But since we have been there I was looking for something else where there is easy train access and can reach other cities nearby. All of these suggestions fit the criteria.
I think Florence will be a long day trip. We will have 3 full days, 4 nights in the region. So, can venture out to at least another city as well. I like Florence but it is the most touristy city I have ever been in and would rather not sleep there.
Part of the issue is that I use Rick's books exclusively to plan and travel and he does not even have any information on some of these suggested cities. So, will check them out online. Just need to settle this cuz then I can book the airfare at a city hopefully nearby!

If you plan to spend a significant amount of time visiting Florence I would stay in Florence. I understand that it's touristy (although not so much after Covid), but you can choose to stay in neighborhoods that are less so and will give you the impression of being in a smaller town. The neighborhoods that fulfill that requirement are in the Oltrarno (beyond the Arno, i.e. south of the River Arno). The Oltrarno neighborhoods are (from West to East): San Frediano, Santo Spirito, San Niccolò. Santo Spirito, is the busier of the three, but conveniently located near Ponte Vecchio, you can find quiet streets in Santo Spirito as well. San Frediano is the quietest, and also a closer walk to the train station, if you plan some day trips from Florence.

A second vote for Arezzo. We spent a week there as our hub and would not hesitate to stay there again.

As much as I LOVE Firenze and have stayed many, many times...I chose a small town (Pistoia) close by for the first portion of my trip this year (mostly due to rising rental cost). Easy/short train to Firenze to see friends and go to some of my favorite places. Arezzo is also very nice and was under serious consideration....As others have mentioned....Fiosole is cute as well as Grieve which are both reachable via bus.

Staying in Siena gives you several options by both bus and train. If you don’t want to stay in Florence, it’s an easy bus (#R131) ride from Siena to Florence. An hour 15 minutes.

From Siena.
These towns are easily accessible by bus and train. Some towns I've combined with others. (B=bus, T=train)
Siena-Colle di Val d'Elsa ( B 30m)-San Gimignano (B 35m)-Siena (T 1H05m)
Siena-Montereggioni (B 18m)-Castellina in Chianti (B 30m)
Siena-Radda in Chianti (B 55m)
Siena-Buonconvento (T 28m)-Monteroni d'Arbia
(T 12m)-Siena
Siena-Rapolano Terme (T 37m)-Asciano Mont Oliveto (T 10m)-Siena (T 26m)
Siena-Sinalunga (T 53m)
Siena-San Quirico d' Orcia (B 50m)
Siena-Pienza ( B 1H05m)
Siena-Certaldo (T 39m)

The bus is located in the upper town, the train in the lower town.

The bus terminal in Siena is at Piazza Antonio Gramsci. There’s a kiosk in the middle that allows you to go down underground, where the ticket office is located.

There is also a bus terminal in lower Siena located with the train terminal. If you purchase your ticket at Piazza Antonio Gramsci ask the agent which location is the terminal. This also applies for the Flixbus.

Wow, what wonderful detailed responses. After much contemplating I have decided Siena is the way to go and side trips from there. Florence we will hit up for one night after Siena since we have to connect there anyway by train to then get down to Sorrento.
Thanks so much, and happy travels to you all!