Thanks for coming back on this. I have got some kind of a resolution - but it wasn’t what I expected!
I tried a number of combinations of the above, but to no avail. What I did try though was Option 3, but using the Matter binding and the Tado X App. I hadn’t expected this to work, I don’t have a TBR, but I’m guessing that the Tado X Receiver is broadcasting on Wifi, even if the TRVs are on Thread.
So I’ve now got 4 channels on each TRV (set point, temp, mode and humidity) and can control them through OH.
I’m going to explore how to put them back into HomeKit through the Integration (I’ve got that working already), so it’s just a bit of test & learn. Still not 100% that I’m using the HK Binding in the right way, but I can park that for now.
Thanks for the input.