If you have access to the loft space, try putting your router up there. You can usually then get it placed centrally which helps to spread WiFi evenly throughout the building. In a lot of older buildings the floors and ceiling are wood / plaster, WiFi passes through this a lot easier than it does through thick brick walls.
The last person we had this debate with was expecting his 2xcAP ax’s to reach around his massive house outbuildings and garage.
Same person continued to slag off the product while buying more of a new product, it beggers belief it really does!
Or replace it with paper, like (old) Japanese houses 
Joking aside, I just saw this https://www.everythingrf.com/tech-resources/waveguides-sizes but I have no idea if installing some waveguides/drilling a few big holes though the wall (and covering them with wallpapers) would make any difference, and I am not in the mood to test that 