I'm not an expert in French law so my words should not be taken seriously. As a French resident you're probably aware of the sedated dying law (medicated death). I believe it was introduced 4-5 years ago. Whether you'd be eligible for it is something only you can figure out. Conditions for euthanasia or medical assistance in dying tend to be very strict. This would be the most peaceful otherwise.
If medical assistance is not possible, then I believe the act of suicide itself is not illegal in France, please check French government website. What may make it illegal is the means and method employed, for eg. Importing banned poison or the weapon involved.
Any peaceful method is generally less harsh if not friendlier with the human body's biochemistry and physiology. Hence, certain drugs are commonly used. If you eliminate the 3 you mentioned then I can't think of anything else, because the efficacy of any other drugs need to ascertained.
Any other method like stabbing, electric shock, hanging are very forcible and traumatic on the body; hanging may be an exception if done precisely. It's not my recommendation though.
I do not know your motivation in asking this question but I hope you have tried to get all possible help to alleviate whatever pain/concerns you have. Under your picture and username, it says you are "Wise". I trust you are. You have been a member for many months and have 200+ messages. You know better. Best wishes. *hugs*