//// Are you sure one is needed? My wifi works all over my garden ////
..... that depends where your router is and the layout of your house.
//// In my experience none of them work. ////
We've got one that solved our problems.
Our router is in our front room and in order for the signal to get to the back garden, it has to go through 4 walls. By the time it gets to the outside world, it's a VERY weak signal, sometimes there's no signal at all.
This is the exact same range extender that I bought from Currys:
https://www.currys.co.uk/gbuk/computing-accessories/networking/wifi-range-extenders/tp-link-re305-wifi-range-extender-ac-1200-dual-band-10172715-pdt.html
This plugs into a socket in the conservatory and we can now get a good signal out in the garden - I can personally vouch for this .... now where's my commission Curry's??