First of all ...there are so many ways to do this...
the fastest way would be to just add the pathfinding behaviour to your player and use that..
making sure that you add out all of the walls etc as obstacles
but because this may not look right..your player would in some places..take the shortest route ..which may mean 'FLYING' in places they shouldnt
to solve this if and only if it suits your game
you would create a maze of blocking sprites that are invisible at run time.
making sure that your character fits between the maze walls as required with no room for "flying"
and of course you would still have to change animations when the player reaches a ladder but this should be easy and not affect the pathfinding at all ..because its just animations not mechanics
one other way could be to mod a platformer sprite and add pathfinding behavior to another object that the platformer 'follows'
basically using the pathfinding object to find the path or waypoints then make the platformer follow the pathfinding objects x po
and if and when the pathfinder moves up or down a floor level..then and only then does the platformer climb
you would need to create a sprite with 'PATHFINDING BEHAVIOUR'
you may as well use the built in features..there is no reason why you cant modify its usage to suit your game
then secondly make your Player controller sprite and add a 'platformer' behaviour or custom movement ( based on your layout above you seem to require this..not 8dir)
the movement speeds of each should be the same for each object so that they cant get away from each other
you could even get the path finding object to spawn waypoint sprites which either drop to the floor or spawn at a fixed height depending on which floor the pathfinder object is currently on and spawn every second or so..
which the platformer then moves to these objects waypoints
these are just some ways...that use the built in pathfinding...
just mod it to suit your needs
its a pretty robust behaviour like all c2 behaviors there is alot more ways to use them than you might think
be flexible...let your mind flow with ideas...do lots of tests/experiments..you will see so many other ways
one of the will suit your game perfectly
hope that helps