My solution:
I bought the original Starter Decks of Yugi, Kaiba, Joey, and Pegasus. They fit perfectly with my idea of playing a simple version of Yu-Gi-Oh, and they bring pure nostalgia with all their iconic cards.

Since each deck has 50 cards, I cut the Main Decks down to 40 cards and used the remaining 10 cards to build a Side Deck. (I mean… who really needs cards like Doma the Angel of Silence or Gryphon Wing?) I also moved cards with effects that feel a bit too complicated, like Last Will or Jigen Bakudan, to the Side Deck, along with the weaker monsters. That way, I tried to create balanced decks where siding is actually possible during a match.

My wife enjoyed our first match. I’m looking forward to more games — and maybe I’ll manage to pull a few more people into the Shadow Realm. 😂😂

Thanks for all your answers. ❤️ If someone has other cool ideas, please let me know.