You've already done the AT, so know what the terrain of the Berkshires, Green Mountains, and White Mountains is like. Obviously that gets a lot more difficult with 2-6 feet of snow on the ground. With the right gear, it is of course doable, but at too high a hassle level for most people.
The Long Trail is the first that came to my mind from your description. Don't expect accommodations anywhere along the trail, like there are in places along the AT in summer. You'll be pretty much alone, except where the trail passes near ski resorts. You'll have more options where to camp than in summer, but much less options for anything other than finding and making your own campsite.
For a tamer and less wild experience, you can try some of the smaller lesser-known trails. I'm from north-central MA, so the ones I'm most familiar with are the M+M and Midstate Trails. Permission to camp may be a issue. These kind of trails cross a lot of private lands with public access rights negotiated. Those rights often do not include camping. If you look at any of these secondary trails, you probably want to secure permission for camping spots in advance.
Then of course there are lots of options in the White Mountains. Some of the huts are still open in winter, usually with just a single caretaker. You won't get a meal and other accommodations like you can in summer, but you can sleep indoors. Check ahead. In this case, contact the AMC at the Pinkham Notch visitor center.
There are lots of beautiful and wild trails in the White Mountains that are not part of the AT. Just get a map and look around. As one of many possible examples, you can park at Lincoln Woods, then take the Wilderness Trail to Bondcliff (my favorite spot in all the White Mountains), Bond, Guyot, the Twins, etc. Or stay in the valleys more easterly. There are many many options.
Another totally different possibility is to do a few day hikes on the many local trails that are all throughout the region. These are harder to find, since there is no larger organization that lists them. For example, my town (Groton, MA) has over 110 miles of trails on over 10 square miles of land open to the public. We have more miles of trails than we do paved roads, but anyone more than a few towns away probably has no idea of that. You'll never be that far from a road or a house, but you will discover some amazingly pretty places. Overnight camping is generally not allowed without advance permission, but these kinds of trails are best done as day adventures anyway. Permission can also be arranged, but that's probably more trouble than it's worth.