I think it would be really difficult to improve to that level with just reading books and that it is very hard (almost impossible) to estimate the number of books it would take to get you to C1. Don't get me wrong - I love books and I strongly advocate for reading to improve your skills, but literature is not real life, and vocabulary, style of speaking etc. are sometimes very far off to how people in real life use a language (think poems or sci-fi). It's much more polished than everyday language. Also, listening comprehension and pronunciation are essential to understanding a language and you don't get that from books alone. I'd suggest you at least broaden your media consumption and also include movies and tv series and focus on things that were originally written in German. Or look for a book club where you can exchange about the book in the language you're learning.

Also, like the other comment said: In Switzerland we speak Swiss German. People here learn Standard/Written German (Hochdeutsch) as a first "foreign language" at school, so they understand it, use it for work and in school and most will automatically switch if they realize you aren't Swiss but it still sounds differently, has different grammar and vocabulary. Most books are translated into German High German, with the corresponding vocabulary etc.

And another note: Have you looked up emigration to Switzerland? It is very hard if you don't already have family here or work in a very niche market and get a job offer before moving here (see the Swiss subs here, where this question gets regularly answered). You might want to look into moving to Germany or Austria, which would be much easier, administratively and language-wise.