It's definitely not Fort Knox, but it's an exterior brick wall. Our house basically has two master bedroom/bathroom suites - the original one which we use as a guestroom and a much larger one that was added on above the garage, which is where we sleep. The wall is pretty thick and well-insulated, and it has a very solid door. When it's closed I virtually can't hear anything in the house. The router is just inside my office at the bottom of the stairs and frankly not very far away. I can pick up the WiFi signal a little but not much and not reliably. I installed the repeater at the top of the stairs and with a fairly clear path to the router. When the bedroom door was open, it was fine. When I closed it, the signal was basically no better than it was without the repeater.
This is what I'm using now. As you can see, it's a pretty cheap-*** product, but what appealed to me is that by going through the electrical wires, it basically nullifies the thick wall problem. And sure enough, it works reasonably well. It's not like plugging directly into the router. We lose a little speed with it, but I run an ethernet cable from the outlet in our bedroom directly into the TV and there's enough speed to stream in HD or 4K without buffering, which is good enough for us. However, our other electronics (phones, Fire Stick, laptop, tablets, etc.) are Wifi only, and it does nothing for them. If I need to do something with my phone, I basically just use data.
If I go mesh, I'd probably try something like this.
