I thought a bit, and I'm surely change the "healthcare" and education.
We are the most unhealthiest people in Europe. While the institutions and healthcare sucks, even if we sunk double the amount won't fix shit. It's the people's mindset. To change this, how they view their health and how they live their lives, their lifestyles... it cannot be done. They do what they do, they do what they grew up with, what they are used to. It takes a whole lotta willpower to change it. Impossible task.
So I'd change the education. How bodies will turn out in our adulthood depends on how we grow up. No sitting at desks whole day in school. More training and sports, outdoor activities. These don't just train body, but good for coordination, and personal interactions, can build teamwork too, and also offer competitive experiences.
Healthier diet, less processed, and less carbs (I don't think dropping carbs entirely is a good idea tho), more meat, diary, nuts, vegetables, and fruits (carbs), only some grain and tubers (but these are needed too).
Instead of filling their heads with data, I'd aim to teach them how to learn. Children are naturally curious about the world (typical why? why? why? questions to their parents), this curiosity needs to be nurtured. So they'll grow up that seeking answers is a natural thing and give them the tools to acquire information. How to use information sources, books, libraries, internet, AND the educational system.
Build education for a lifetime. Humans can learn for many decades, it's a lifelong process. So don't just cram all that into childhood, it's useless since most of the children learn only the fraction of that. On the other hand they learn to hate school, teachers, and learning.
Anyway raising children into grownups who pursue active lifestyle and mindful about their diets, and who are oriented to learn new things.
I would not expect 100% success stories but damn sure would get a better "livestock" in a generation than what we have now.
I think this would need about 30 years, from there it could be self-sustainable if the new generation finds it a good idea to preserve it. If not, well I could not stop them.
>Leave Eurozone
So get the old currency back? What was it?
That is a real question for sure.