Well done you for adopting from theSPA.
Insuring your dog is uncommon in France - remarkably since they insure everything else! And often has a cut off of 8 years old.
We don’t bother, and out tyke has had many scrapes but thankfully nothing that has broke the bank. And 3rd party liability is included in your house insurance, so that important aspect is covered.
The only one I have ever heard recommended is this one.