Besides Water/Ground, the only other option that fits is Bug/Steel (weak to Fire).
On the resistance side, Mimikyu's Ghost/Fairy typing gives it three immunities and the double resistance to Bug, but no simple resistances. If you don't count the immunities as resistances, that works, as does Water Absorb Lapras (turning the simple Water resistance into an immunity, where the typing's only other resistance is a double to Ice) and even Air Balloon Flapple at least until the balloon pops (Grass/Dragon actually gets three double resists, on Grass, Water, and Electric, and its only single is to Ground which gets immunized by the balloon).
Also if you don't count immunities as resistances, pure Normal (Rattata etc.) as well as Psychic/Dark (Malamar) have no resistances whatsoever, so you can vacuously say that all of its resistances are doubles, or even triples for that matter.
