Repeaters are awful. It’s best to have multiple access points instead. One simple solution is to deactivate wifi in your ISPs router, and add your own APs instead, possibly via a switch.

I ran some cables throughout my house and bought a 3-pach of Aruba AP22. Wired them into a PoE switch, which in turn connects to my router (I managed to replace my ISPs router, but that’s besides the point). Works like a charm.