I have a start for this trip: Milan for 2 nights then??? go to Venice for a for a couple nights thinking over New Years Eve but would like a couple of other towns to stay or base ourselves out of. Would love to hit a Christmas market if there are any still open. 4 of us are traveling. We have been to Rome, all over Tuscany and Florence, we loved the latter two and checked Rome off our list. We are active and move fairly fast. Colder weather is not an issue for us. Would love to find town(s) that we can easily walk to eat and see the sights as we will not have a car, we will be using train and private transfers. Any guides or drivers you loved please feel free to share names and contacts. Thanks in advance.
Do you like snow? Go to Ortisei in the Dolomites fro a few days. Charming town.
Skip Milan at the start. Assuming you are flying out of there as well? Take the train directly to Venice. Give it 3 nights, 27-28-29. On the 30th. Make your way to Ortisei as Suki suggests. It’s gonna be high season but so charming and the ability to take gondola lifts up and even do some walking (or take a horse-drawn sleigh) in the Alpe di SIusi. (LMK if you want details.) We stayed one Christmas at Hotel Albion just outside of Ortisei and loved it. Half-Pension meaning two meals a day included, great spa facilities, and a shuttle into Ortisei on demand. Dec 30-31 and Jan 1-2. Make it four nights so you can truly enjoy the little towns of the Val Gardena.
Now you have Jan 3-4-5 available. You’ll probably have to spend the 5th in Milano. Perhaps the 2 nights Jan 3-4 in Verona, which is on your route to Milano.
Just some thoughts on a not-too-fast pace.