Nicolas,
I found this
https://www.aopa.org/travel/internat.../transatlantic which has some good information and mentions relaying position reports through airliners in the higher flight levels.
I had an email exchange with Hermann who I mentioned in post # 26. He said, "It looks like on this tour I only meet nice and helpful people and this makes me really really happy!" He's a fellow airline pilot, and I suspect that he would be glad to help with your questions on survival gear, country specific procedures, etc. If you are not able to contact him via the link, email me (post # 26 also), and I'll try to put you in touch with him.
Cheers, David
RV-6A KBTF