I don't have any experience with French TV standards or Freeview boxes so I can't give any specific advice. However in general, you've got the same problem that happened when 1st & 2nd generation video game consoles and DVD players first came out: how to get a composite A/V signal into a TV that only accepts RF input.
The solution was (and is) to use an RF Modulator. Something like these:
The two RF modulators above are designed to work with older US televisions (NTSC), so they are not going to work for you in Paris unless your Sony TV is an American model. But there has got to be an equivalent solution for French TVs and I can't imagine it would be horribly difficult to find.
I did a quick Google search and found this page, you might find it useful:
Regarding the composite jacks on the back of your Freeview box, they might work but there's no way to know for certain unless you try it or have a manual to read. From what little I read while searching around, it seems that some Freeview boxes have RF modulators built in (which could explain those composite jacks) but most don't.
Another possibility might be to find a cheap VCR that has the correct inputs to accommodate your SlingCatcher and outputs to match your TV. People do that all the time, especially with the Slingbox AV and SOLO models. Again, my experience is limited to US-spec equipment, but it's reasonable that European-spec equipment would have a similar way to solve the common problem.
Hope this helps get you moving in the right direction. I think Google is your friend on this one.
Good luck !