Unfortunately WIFI isn't a perfect solution. There are issues with range and the composition of your house/flat, interferance from neighbours, walls and metal mesh will also degrade or even block your WIFI signal. In such cases you will need a WIFI repeater which will, as it says on the tin repeat the existing signal strengthing it.
Here is a link to give a big more information:
Wi-Fi Extender vs. Booster vs. Repeater: What's the Difference? (howtogeek.com)
Sky do sell their own repeaters:
Sky Broadband Boost | Sky Help | Sky.com
They cost more but are a simpler solution. My advice is how technically confident are you? If not go with sky otherwise shop around for a cheaper deal.
