In addition to Skills Forward, we recommend looking at Corbettmaths too. It’s completely free and a really good way to build and test your skills. It’s aimed at GCSE, but the skills are the same. The worksheets are linked with really good videos and once you have worked through them, you can click on the answers to see how you get on.
There is also this website, which is mostly free to access, so would be worth exploring:
Finally, the BBC have recently created a Bitesize revision site for Functional Skills which might be worth looking at too: