If you’ve not got past the first part of the original post, then you’ll not see that I’ve substantially tidied it up since my initial prototype in my old house (the “dangling wires” photos)!
I’ve now run everything hidden, I have some temperature sensors in the ceiling, I’m also able to use any other temperature-reporting devices I wish - I can now even control it via Google Assistant and Amazon Alexa for hands-free operation.
If you don’t want to go to this level, then I would also suggest looking at Drayton Wiser - although this is a remotely accessible service, I think that you can also control it internally from openHAB without needing their cloud service… somewhere later in that linked thread should give you some further details.