Collision on the bottom?

Hello,

Trying to make a 3D platformer.
Got a stick figure with a box collider on it.
When he is on on the “ground” or a platform, he stops falling.

The best way I can figure to do this is to check if there is something colliding with the bottom of the collider. Except I have no idea how to specifically check the bottom during collision.

The other object is to just have another box collider only on the bottom, but that seems hacky.

Add two colliders to the platform, one above and one below (that is just a trigger). When the below trigger “enters” you disable the above and vice-versa.