Many thanks to all of you who have taken time to reply to my post and my apologies for not having been able to answer sooner!
Your suggestions have been most helpful! Some of the books suggested I have already read:
Vargas : one of my favourite crime writers
Immortelle randonnée : a delightful read! It is a book I often offer to friends for their birthday.
Priez pour nous à Compostelle : I was blessed to read this book before my very first Camino and it helped me immensely not only to understand the history of the Way, but medieval society in general.
RLS’s "Travels with a Donkey in the Cévennes" and the Martin Walker novels I will leave for when I come back home, because I want to limit myself to books in French for the duration of my walk.
Mention of "Travels with a Donkey in the Cévennes" reminds me of a book about the Voie du Puy which I can warmly recommend: "Travels with a stick", by a Scottish Presbyterian minister called Richard Frazer. See here my review of his book:
https://www.caminodesantiago.me/community/threads/travels-with-a-stick-by-richard-frazer.66666/
"Vestibule des causes perdues" I will certainly buy, but for my wife, who cannot accompany me physically.
For her too I will buy, if I can find it, "Mourjou", for she is a keen cook.
Thank you all once again for your help!