At 78 it's a bit late to change my nationality so I applied for a 'Titre de Sejour, basis 'European Citizen'. If you have lived in France continuously for five years and can support yourself this CANNOT BE REFUSED. There is even an EU department that will support you if you are refused.
The documents that you need SHOULD be listed on your Department's web site. They are also listed on the Ministry of the Interior's site. You will find that they conflict and it is probable that the locals will add a few more requirements of their own. I overcame my difficulty by writing to the President. It was amazing how quickly everything went after that.
It is very important that they understand that it is a European Citizen's TdS that you want as there is no application form and staff don't seem to be well informed, perhaps before the threat of Brexit it was not needed, I have lived here for twelve years, paid my imports sur revenues, belong to the French health system, and voted in local elections without any questions.
A last point. If you check on your situation in the French Social care system you will find that it is limited to French Citizens and E.U. CITIZENS. As we are about to loose that citizenship it might be wise to consider your VOTE in the coming election. My experience over the past eighteen months is that the present government doesn't understand our situation or doesn't care. The only answers from my MP or government officials is either wrong or 'I don't know'