I'm confused. Unless you've (very unusually) got a TV set that's (only) got a Freesat receiver inside it then, as long as it's not more than about 15 years old, it must have a Freeview tuner in it. (You'd need to get an aerial installed to be able to use it but the tuner must be there).
However if you've already got a Sky box (and satellite dish) then you'll still be able to receive all of the channels listed in this link when you cancel your Sky subscription:
https://en.wikipedia.org/wiki/List_of_free-to-air_channels_at_28%C2%B0E
You'll lose the recording facility though. (You'll also lose any recordings you've already made).
The simplest solution for you (and the one that's possibly the most common among people who're in the same situation as you're now in) is to replace your Sky box with a Humax Freesat one:
http://www.argos.co.uk/product/4558730