[vel0city]

I'd highly recommend looking at just getting a wired AP to put in the basement and have it ceiling mounted. It really depends on how your house was designed, but it could be relatively easy to drop a cable down from an above floor to the ceiling. You'll get much better performance having a wire carrying the signal than trying to do WiFi mesh setups, especially when you're trying to cover an area that already has terrible WiFi performance.

[mook]

In my experience even Ethernet over powerline is better than using WiFi mesh, since there's still a wire, even if it's noisy. That is, it provided a more stable connection, even if the peak speed is not theoretically as fast.

Your mileage may vary.

[vel0city]

Your mileage can definitely vary with Powerline Ethernet adapters. When they work they're amazing, when they stop working it can be rather annoying. Most don't have any real feedback other than a small handful of LEDs on the device. I've had several different models from different vendors over the years using a few of the various revisions of standard and different electrical system setups. They would usually work pretty well for weeks, then suddenly lose their sync for unknown reasons requiring a hard reset. Often this happens right when you're in the middle of watching a movie or playing a game, requiring you to stop what you're doing, unplug both devices, wait a few seconds, plug both back in, and it magically starts working fine again. I've had that experience on all of the units I've used. It has been about 5 years since the last time I used one, I'm sure they've constantly had improvements.

That said though when they work I got pretty much the rated speeds all the time without any intermediate dropouts or other issues. Stupid simple to use, just plug both sides in and suddenly network. This was sometimes even without both units being on the same circuit, but at least one of the legs had a decently short run to the electrical panel.