Plugin to make site mobile compatible?

A site I manager for a friend https://www.franchsieyourbusiness.ie is not easy to read on a mobile device. He’s on to me asking for a plugin etc that will make it mobile ready.

Now I know no plugin is going to create a perfect mobile site, I just want any that will take the content and put it in a mobile fashion. Any way in which it can be customised like with a logo etc would be great

I tried to get someone to do it but it would not work. Can anyone advice a very easu plugin that can do this?
Thanks