Is it possible to look around within your current company to see if there is any internal opportunity?
Also, one choice is to directly talk to your German boss, telling him you would like to take more responsibility on business side, asking his idea - what kind of career path you can get in this current team, and if there is an opportunity to move on, if so, if he can work with you on a plan.
A more risky route - it seems like your boss's boss knows you well too. If you can not get good answers from your German boss, you may ask to set up a mentorship with your boss'es boss, and asking for guidance in career path. But this is sensitive and risky.
- just my 2 cents. good luck!