Hi Karl, if I understood you perfectly, you need the German B1 Certificate to apply for a permanent residency in Germany, right. If that's the case I would recommend you take the TELC exam at the Hartnackschule in Berlin, specically the DTZ-Deutschest für Zuwanderer/Intergrattionskurs.
You can get some preparatory materials from the telc website.
I strongly recommend you use the +Babbel Application. It's not a free App. But I would say it's an excellent app. Give a it try. Approx. 56 € for a six months subscription.
All the Best!