In the morning I start my 26 hour ride towards home.
Zesen Trans that has very negative reviews turns out to be a decent company, at least today in my case. The bus looks okay, people are friendly, no-one demands any additional payments and in the end the bus is only around half an hour late. That means I have no trouble switching to my second bus in Warsaw. The second bus is Flixbus, undoubtedly the most comfortable from the selection of buses that I have experienced on this trip.
I used this website www.busliniensuche.de to search for bus connections but it is probably wise to google the individual service providers because the site is only a middleman.