It sounds simple in theory, but for the light switches and relays I’d need to get in an electrician, and I’m just not that invested yet. I don’t have bulbs I can swap out, as my lights don’t have bulbs. That leaves smart plugs and that last one you linked, the gateway.
Smart plugs are annoying. They are big and bulky, the plugs fall out of the wall easily when they get bumped by kids, and it’s an annoying extra thing for anyone wanting to use that socket.
That last link you have looks interesting. It doesn’t state what the range is, but the reviews have lots of comments about the great range. That might be an option. Any idea what kind of range it has? I need to make it about 10-15 metres and through 3 walls, so I suspect it’s a bit of a stretch but it would still probably greatly reduce the number of devices I need in between.