SD has it, in a nutshell.
I used to have three boxes in this cottage: an ADSL modem with one RJ45 out port, a router - one "in" port and 4 out, and a WiFi access box. All were "good brand", all worked - sort of. Up time was 99.9% but once the WiFi dropped, I had to reset the laptop. I never did find which box was hiccuping.
I replaced the lot with one box doing all that stuff, and it's never even sneezed in the year or so since then. £50 well spent.
Check the reviews and "customer complaints", and pick a good one, You won't regret it.