Recommendations for improving network coverage? - eviltoast

So my mother currently just has the default router provided by her ISP which is not providing enough coverage throughout her ground floor flat.

I’ve been looking for replacements in order to improve the situation, but unfortunately I’m not very proficient with networking solutions and I’m getting a tad overwhelmed with all the options, so I was hoping that somebody with a bit more knowledge might have some recommendations.

She doesn’t have any ethernet ports (aside from where the router is of course), and no coax either, so MoCa is out of the question. I was thinking perhaps getting an Eero network and just using wireless backhaul, since she’s not a techy and I don’t want to be called up constantly to help with issues.

Really just looking for something that requires no/very little maintenance and would be able to reliably cover her two bed, ground floor flat. Cheaper would be better, not really flush with money unfortunately!