So the weather has improved, and I've got the plastic trim off the seat frames to investigate further. The drivers side seat has a single '8 plug' module and the passenger seat has a smaller '3 plug' module. I was expecting the drivers side to have the smaller 3 plug module too, as this is for the electric heating. Clearly, one module can serve two seats.
The seat module carrier in my F07N doesn't resemble that in the online manual I refer to, so I wasnt able to see which module the driver seat uses. This job would be far easier, if I took the seats out, but I don't want to go there yet.
So I know I need an 8 plug seat module, as this is where all the positions for the various drives and sensors are stored. Plus, I'll need a new wiring loom between the seat position switch cluster, the new seat module. I didn't think to make a note of the drivers wiring loom, as I was rummaging under the seats, so that is a task for next time. RealOEM doesn't seem to offer a loom with 6 connectors (Although the module has 8 connectors, 2 arent used unless you have active ventilation / massage functionality) to run between the seat module and the seat position switch, but I might have missed it.
So the obvious way forward, simplistically, is a new seat module, identical to the existing drivers side, plus an identical wiring loom between seat module and seat position switch. Some of the pin assignments will need changing ( this is how the modules differentiate between driver and passenger, since there isn't a driver or passenger specific module).
Depending on what seat module I need, new ones cost between £177 and £277 new. Second hand they can vary between between £50-£150. I haven't yet seen any seat modules of the types I'm interested in from 2016 onwards. Most are between 2009 and 2012. So the new route looks most likely. Until I find out the wiring loom reference, I won't know what the likely cost for that is either.
So progress is still slow on this🙄🤣