Repeater = takes existing wifi signal and er repeats it. Downside is if your wifi signal is weak/nosiy then it might be a bit chocolate teapot. Last resort for me if I was in your situation.
Extender/WAP. Runs on a cable, ethernet usually. So you could run an ethernet cable from your router to a point in your house near the garden with a PoE (power over ethernet) injector at the router end to power the Wireless Access Point. You can get skinny round or flat CAT6(A) ethernet cables on Amazon e.g. Monoprice Slimrun.
Powerline
Running two PL plugs via the mains wiring in your house. One plug at the router end with a short ethernet cable to it, the second cable/WiFi plug at the destination end. AV2 is a decent spec but you won't get anywhere near the headline rates in the real world, which may not be an issue for just a bit of web surfing.
MoCA
Same as powerline but ethernet over
co-ax cable. Better performance than Powerline, almost as good as straight ethernet. If you've already got co-ax installed from a previous AV setup like NTL/Virgin then should be good to go.
https://mocalliance.org/index.php