You seem fixated on small towns, and that’s great. But that means the rest of this may not go over well.
First, a lot of your list are tourist towns so escaping tourism may be a tad difficult in a smaller environment. It will just require more research.
So you are talking about 75 days more or less. The places you mention are 3 or 4 day as a tourist sort of places, so maybe twice that if you plan to just hang. I would have to do 10 of them or go crazy. Just so much time I can spend looking into the eyes of my significant other.
Think about a typical day in one of those towns. Plan maybe a week in some detail then ask yourself, “is that what I want” or was I overly romanticizing it?
Another way to approach this might be to rethink a large city or two in the mix. Lets say you have been to London and as a good traveler you stayed in the most opportunistic location for tourism, and you did it all.
Well, that’s not this trip. Now you want to find the neighborhood that is where all the up and coming are moving to. The one with good restaurants, parks, interesting architecture (new and old maybe). The clean storybook neighborhood.
You live like a local there (okay, bring it on), but now you can take the commuter train into the center for the theater one night a special meal another, maybe a local event that tourists don’t do. Each time returning to your home in the suburbs.
Maybe one trip is a longer haul to a different city for a few nights. Doing all of this you really are doing what locals do. It’s what you maybe are doing in your home town in the US (I assume US). But the options in-between extended periods of “hanging” multiply exponentially.
Remember most (many? Not to overly generalize) suburbs in European cities are not like those in the US, they tend to be more town or village in nature …. Or many are and those are the ones you hunt for.
Try a few breakfast places then go back to the one you like the best and keep returning. Ask the waiter his name and then the next time greet him by name. 9 our of 10 times you will end up with someone that will welcome you back by name and share a lot of thoughts about life there with you. I have talked a few into doing this sort of thing here, and they had a good time. The comments also included “relaxed” and “comfortable” one never stopped talking about decompressing, what ever the heck that means. But you can do it in a hundred cities.
The biggest hurdle is finding the neighborhood. For that you need a local to advise you. The same local can direct you to a local gallery opening or a visiting chef night in a restaurant or maybe a wine tasting. Better if you can swing a neighborhood tour by a local. I don’t mean walking down the street with someone pointing things out, I mean tagging along for a day in the-life. We have some on the forum that live in Germany and France and Spain and ….. maybe they can give you leads.
Suburb in New Larger City (20 days), New Small City (10 days), New Small City (10 days), Return to a Large City you know a little, but the suburbs this time (20 days), New Small City (10 days) = 70 days but nothing rushed.
And if you buy it open jaw you only have to be at the first and last location and if your mood changes you can stay longer or move on sooner and not worry.