I have my 17 pullets (a couple have recently started laying, so pullets & hens, now)

in a 10’x12’ metal shed with sliding barn doors.
It’s been as cold as -14 Fahrenheit so far this winter. The only problem I’ve had with their comfort happened shortly after moving them in from their very cute, very expensive, very labor-intensive smaller coop. I came out to bring them their breakfast the next morning and found them pecking at little rivulets of water running down the walls. Oops!
We (DH and I) cut holes in the gable ends and installed screened vents... one on each end wall. No more condensation. All that moisture, in that generously sized space, came from 17 little chickens! There was never any moisture when it housed tools and a few mice. Some of the girls have single combs (Australorps & Orpingtons), but most have rose or strawberry combs more suitable for cold-climate birds. None of them have any frost damage.
Technically the first coop is nearly big enough for them, but that’s assuming they’ll at least be out in their run in daylight hours. Much of the winter, that’s not going to happen (they’re freaked out about snow and wind... imagine that!), so they do need space to run around inside. Really, once you add a nice ladder perch (put the 2x4s with the broad side up so they can keep their toes warm by sitting on them) and nesting boxes, it’s not that much room.
I’m doing deep bedding, but it’s not composting for me. The new coop was formerly a tool shed and has a plywood floor so that’s probably just as well, though decomposition might have given them some warmth. It seems to me their little bodies do generate a BTU or so, plus I include straw into the mix of bedding. Straw retains some heat, since it’s hollow. Every little bit...
Your situation sounds just fine to me... of course when you start thinking you need more and different chickens, maybe some heritage turkeys, possibly a Christmas goose or four... it’s gonna start looking mighty skimpy mighty quick.