Have you had an email from the UK government explaining what you need to do?

[graham]

There’s another similar thread running with information on this subject John here:

British French “Resident” traveling back to France in the new year

Youshouldn’t need masses of documents, one can easily get an attestation de residence for free from the mairie - mine’s a simple statement of my address in the commune with the maire’s signature, dated and over-stamped in a couple of places.