Looks like the WiFi mesh was the right solution for the horrendous WiFi coverage in the new flat.

3 little mesh routers later, and I have excellent speeds everywhere on both floors, and, more importantly in the office where I edit / publish stuff.

@thelinuxEXP do you use a desktop in your office. I wonder if powerline adapterd would be more useful in sich a situation
@engravecavedave Both desktop and laptop, but on a 1960s flat with old wiring, power line adapters gave me a 10th of the mesh WiFi speeds :)