Strictly speaking to be truly professional as I'm sure you know, you need to be registered with something. Even a member of the BACP or similar would do I imagine. All I do is state clearly that I'm a member of the BACP ( all that requires is a yearly payment) and that I adhere to their code of practice / ethics etc and make a personal statement, mentioning insurance, supervision. CPD and personal objectives etc.
Counselling for Relate (Scotland) was easy as they did all the donkey work. I try to follow their example. It's not perfect and perhaps I am open to criticism but it has worked for me for the past few years here. I don't really counsel enough to make it a business. I only ever had one problem client who screamed at me for 4 hours as I tried to prevent her from driving home until I had calmed her down!!!! Apart from that all my clients have been lovely and only too pleased to be able to talk about their issues in a safe environment. As I said before, I choose my clients carefully and hope that will be enough to protect both them and me.
There are people who claim to be all sorts of things and they have no qualifications etc and seem to get away with it here in France. That's not for me. But on the other hand France isn't the easiest place to run a small business and you need to be creative. If your local doctor has faith in you and is prepared to send clients to you based on what you can show as evidence of your learning (you have a PhD after all and much more qualified than me), I don't see any problems for you to practice here.
An 'Association' seems to be the way forward if you want to be legal. A 'Micro-Entrepreneur' would be the way forward if you are under 65 and require health cover at the basic level. Maybe a look into the requirements of being a therapist under the Micro-Entrepreneur' regime may be an idea.
Like most things in France it can be very complicated but also the complications themselves make things possible. If you see what I mean?
Anyway, I wish you luck. Your help IS needed here in France and ultimately all you need to be is Non-judgmental, Congruent and Empathetic. As if you didn't know LOL.
PS the Counselling in France website has been going for years and I'm sure they can help you with any worries you may have.