Have a look at jauce.com, but you should have a general idea what to look for. Dictum.com has a curated offer, but idk what shopping will cost you from Germany, but they for real quality. www.dictum.com/en/sharpening-e
And what you need depends on many factors: how many knives is worth how much to invest? I like that one for basic needs: dictum.com/…/cerax-combination-stone-without-base… Of you want to sharpen Japanese steel, like shiro gami or aogami, maybe something with softer bindings, tiger stones for example. Chips in the blade? Diamond stone, only mono-crystalline ones. Here’s an inexpensive set I can recommen: dictum.com/…/m-power-tools-dc-shapingsharpening-b… Maybe there were vendors for M. Power tool diamond stones in your vicinity.