so getting a carte de séjour should be relatively painless
Don't you believe it .... get ready for a massive paper-chase, once you have accommodation in France and can prove it - usually by a current utilities bill as a minimum - and at least a 5 months' wait depending on which
Préfecture is processing your application. Fewer problems ahead if you're over 60.
And getting a carte de séjour will only get you 5 years stay, then a further renewal, then ................... well nobody knows
even now what will happen to current carte de séjour holders holding UK passports so don't pin your hopes on it becoming a 'get out of jail free' card or the magic key to continued employment.
And please remember that HMRC are still keen to collect tax from you and have a dual taxation treaty with the French government which will probably still stand after an eventual Brexit.