I’m familiar with the absolute basics of networking, but very little surrounding wifi.

I’m current using the modem-router-AP provided by my ISP, along with a couple repeaters. This isn’t working well, and in areas of my house further away from my main AP, packet loss is often around 20% - near unusable. How should I improve this?

I can run some wires (within reason), and have multiple spare routers-APs to work with. I can also buy something new off the shelf if needed, but don’t want to spend more than I have to. What would be the approach I should use? Like, is there a particular type of extender I should be using, or can I use multiple routers as a mesh or something?