@Marc **********
The monthly pension of at least 2.000 € Euros is only specific to the Thai Embassy in Paris for them to issue a Single Entry Non–O (based on over age 50 years old "retirement") Thai E–Visa
Now, using that Thai E–Visa Non–O from the Thai Embassy in Paris to make entry into Thailand, your local Thai Immigration Office in-country (in Thailand) will have different requirements for an Extension and you would be required to start again with ฿ 800.000 Baht, as you wish to use the ฿ 65.000 Baht/month method can only be done on a subsequent (year 2) Extension =
if you let your "year 1" Extension of Stay expire and then afterwards, go obtain a new Non–O E–Visa at the Thai Embassy in Paris, then that resets everything regarding Extensions of Stay obtained (only available in-country, in Thailand) and starting all over with 800k for Year 1, then could be able for the Year 2 Extension of 65k/month....