Nothing to do with selling... but I received a letter asking me to get documents similarly certified..... and phoned and explained that ....here... it was quite normal for documents to be Certified by a Government Official at the local Government Offices and they said such would be acceptable.
I had all the documents "Certified as True copies of original" by the Maire at the Mairie, with all the signatures, stamps and flourishes... and enclosed a covering letter explaining everything, yet again. All went well.
If you are known at your Mairie, they could also do you a letter confirming you are, who you say you are...
Perhaps you could discuss this to your Solicitor..
Proof of your address is usually an Electricity Bill...or other Utilities.. or perhaps your Impot , Tax d'habitation etc.. all official documents, after all.