Lots, options are good, and there are plenty. Since you're in Germany, maybe take a look at Aqor, pretty much a Halcyon knockoff, made in China, distributed out of Germany, pretty decent quality from what I've seen. Depending on what area of Germany you're in, may be a local dealer nearby.Are there any other brands beside xDeep or TechLine? I mean, probably but since I only read about these 2, I should stay with these 2.
Now.. Single or Dual Bladder? How much Volume? This might be a question where more info about myself is necessary.
Halcyon gear is very high quality, with the price tag to match, and has EU dealers.
There are some EU-specific smaller brands like DTD and DirZone which, if I had to guess, are probably made in the same factory in china as alot of the other smaller brands, no experience with either, apologies if I'm wrong.
Apeks gear is very high quality and should be significantly cheaper over there than it is here in the US. A few of my local buddies dive Apeks BP&W, quality is as good as it gets.
Definitely single bladder. Dual bladder is pretty much a specialty product for those who insist on diving heavy steel doubles in a wetsuit. Instead, carry a small SMB with you that you can use for alternate flotation at the surface, should always have one while diving regardless.