Here's the lounge process, but we've had to do 4 external walls so far.
Bought a Zehnder ComfoAir 350 for £500 (deal). We have a radial ducting plan which involves lowering a (tall) corridor ceiling by 20cm to move against the joist direction... fingers crossed.
looks fab! wish we had the foresight to do something similar, only used insulated plasterboard to the back of the house in the end, though suppose that's better than nowt.
a very noble goal, i both do and don't envy you..! photos always welcome too :)