[Astromancer]

As much as I prefer the idea of "the helm let's you jump to the Astral plane at any time." it simply can't work that way. Spelljamming ships can run out of good air. There are spells to restore air quality. None of which makes sense if you can just jump to the Astral Plane at anytime and refresh your air supply.

There has to be a point of transition between wildspace and astral space.

Without that limitation, why worry about air?