It seems that there are no day tickets including gvb and a single NS train travel to Amsterdam Centraal (excluding schipol).
So till now my research says: "The Amsterdam Travel Ticket" for 3 days at 25 euro + paper ticket Halweg-Zwanenbug <-> Amsterdam.
Am I correct? Are there any NS day tickets for these two stations?
(anonymous OV card is out of question, until the minimum 20 euro charge is required)
EDIT: thanks for the replies. I realized that I was looking for transport zones, like the a-b-c in Berlin. Amsterdam doesn't have it, and the only option is what @JaneDoe1337 says: gvb for 21 euro/96 hours plus return tickets for the NS trips. My gf correctly says that going downtown 2 times per day in two means almost 32 euro per day. With this knowledge it's probably less expensive to rent a house inside the gvb zone. Anyway, we cross the fingers for good weather and bike rental :)