For clarification:
Freeview is a totally different system to anything offered via satellite and should be IGNORED here (unless you're planning on switching to take your TV services from a terrestrial aerial, rather than from a satellite dish).
A Sky box without a valid subscription (or a 'Freesat from Sky' card) becomes a generic satellite receiver, giving you access to all of these 'Freee to Air' channels:
https://en.wikipedia.org/wiki/List_of_free-to-air_channels_at_28%C2%B0E
'Freesat' is a system which actually offers you a
subset of the channels in that list by default (although you can add the other channels manually). It's accessed by special 'Freesat' set-top boxes (or by using a TV set with a Freesat tuner built into it). It also gives you an EPG (electronic programme guide) but not a great deal more.
'Freesat from Sky' is, confusingly, NOT the same as 'Freesat'. You get it by paying a one-off fee for a viewing card, which gives you all of the 'Free to Air' (unencrypted) channels in my Wikipedia link above (which you'd get without the card anyway) PLUS a very small number of 'Free to View' (encrypted) channels:
https://en.wikipedia.org/wiki/Freesat_from_Sky#Extra_channels