I dont understand why youd want to move between layers at all. If a layer is over the main play layer then that layer should be considered to be a "not much of anything is higher into the 'sky' than this" the exception being sky/clouds etc.
That means under pretty much every thinkable circumstance the player should always be under it, thus its on another layer.
Same for the ground layers. The player will most likely never be below that layer so consider it that way all the time.
Its like this:
------ arbitrary number of sky layers for fancy foreground effects
------ Top layer 1
------ Top layer 2
------ Player layer
------ Bottom layer 1
------ Bottom layer 2
Everything in the top layers is always above the player. You dont really need 2 of em but you might have a use for 2 its possible. Those layers consist of ONLY objects the player should ALWAYS be under or behind like bridges or the high part of a wall section you dont collide with.
The bottom layers (again you might not really need 2) is for things the player should ALWAYS be on top of, ground dirt roads etc.
The middle Player layer is where anythin the player can overlap should be and thats the only layer your z-sorting should be needed on.
The only time the player should change layers is for things like a bridge you can walk under and across. But that kinda complicated topdown collision doesnt have anythin to do with this