There's no such thing as a "high power router", power output by devices is regulated by design so you cover larger areas with more access points (the typical consumer router contains a router, a switch and an access point.) The trick for you is getting some APs (or at least one) further up in your house. If you can't run ethernet, you could perhaps use MoCa, which is the ethernet network protocol carried over coax cables with adapters at each end.

Mikrotik is not famous for simplicity. Neither is Ubiquiti UniFi unless the defaults work for you. TP-Link's Omada is a decent choice; it and Ubiquiti use a central controller for "single pane of glass" management of the network.

If the wiring (ethernet or over coax) don't work for you, a good mesh system would help. The mesh relays from the router (base unit) to APs (satellites, or "mesh points") over radio. It can be slower but it does allow you to sometimes reach further when you cannot (or don't want to) wire your network.