Every grocery store will have " laktose frei Milch." If Aldi or lidl doesn't have it for some reason..Rewe, Tangelman and Edeka will surely have it. I'm in Munich and it is very easy to find here so I don't think Berlin will be much different.

Health food stores like Deans or Alnatura will also have it.

You can also easily find lactose free cream cheese and other options