Combat Map: Water Park Diagnostics
Aquaman feels robust developing simply a relationship with Mera.
However, the introduction of Aqualad and Aquagirl makes for interesting storytelling --- perhaps at least for adventures involving these two young sidekick-oriented heroes going on special missions.
Batman (DC Comics) obviously benefits from his sidekick Robin, and Green Hornet (DC Comics) benefits from his sidekick Kato, but the sea is so vast and mysterious that we can imagine a titular superhero like Aquaman carrying his weight just with a life-partner like Mera.
I think when you consider Aquaman tackling the invasive Black Manta, perhaps his most unusual nemesis, you have to consider how the arena/environment of the water makes for pensive combat, and it can be argued that a sidekick could face real danger.