Depending on your definition of "monitor", I did last winter. I paid very close attention to temperature, humidity, and airflow. I used equipment to measure it only a few times, though.
I have an unconventional design that many people (some in other venues, like real life) told me wouldn't work. I paid close attention to see whether I needed to change to my back up plan. I also measured on several days to communicate more precisely than "I can tell", lol. And I'm in the nerdy overthinker camp too.
Anyway,
here is the thread with the results
post 145 and 153 and several later.
The short version is when the weather service said it was about 19.7F and about 61.2% relative humidity outside, inside measured 35F and 34% relative humidity. I only had an indoor "humidity monitor" so it wouldn't register below freezing.
I think that is accurate based on how when and how fast the snow melted off my boots inside when it was below 20F outside. And when my face would sting outside vs inside and when the snow would crunch when you walked on it - last January I could have told you precisely what temperatures those happened, it was really consistent but I don't remember now.
Either way, zero signs of frost damage to even the leghorns' combs or wattles through the coldest months. We reached low single digits for a few days and sustained below 15 for weeks straight.
I would call it "reached" warmer than 5-10 degrees F rather than "stayed". It was only warmer in the daytime.
I did it by leaving a 4' wide, 7' high door open day and night all year. You jested about that in a later post but it did work. Because the other three walls were closed off, there was no draft. Because there was such a wide opening, there was lots of gentle air flow. Edit to add: perhaps I should note that proportions do matter - 4' open with a 10' depth works. Based on being in three-sided livestock shelters, woodsheds, and such there is a perhaps surprisingly wide window of what works but at some point it will be too deep or too shallow to work well with a given width. I don't know where those lines are.
I have no electricity (neither wired nor solar) in the building; the warmth is from the sun shining on the bedding and such.
I don't think this is the only good way to do winter but it is "a" good way.
The pictures are from last winter except the one from last fall. The fall picture is because it shows how the sun comes in; I have some from winter showing it coming even further into the coop because the sun is lower but this shows my chicks in better poses. In the sunny winter ones, they have their heads bent into their feed dish.
It gets a lot warmer inside on sunny days, of course. I don't think it matters much. They seemed as comfortable either way based on their attitudes and activities and lack of frost damage. In the summer, they have some shade from trees and I open the windows and eaves too, so the sun shining in isn't too much.