Plan D seems to have eliminated the stairs. Is there a different access point? Have you played with making the storage the closet and the closet the office? that seems it would eliminate the need for a vestibule. Not sure of all the details in that, but a vestibule seems like a waste of space.

Here's a very crude version of the idea. Orange lines are what is eliminated, blue lines are new walls or doors. Still a lot of doors, but not so much wasted space. You could even make the office larger into the closet or have a closet for the office along the wall between the office and new closet.

Here is an idea similar to plan D. Moving the doorway to the bathroom and enlarging the vestibule gives you a couple more options and does not seem so constricted.

You can have a door between the vestibule and bedroom to allow use of the office, closet and bathroom at night with out light getting into the bedroom.

You could eliminate the door into the bathroom if you keep a door on the toilet area. Or you could keep the door on the bathroom and eliminate the door on the toilet area. Or you could keep all the doors.

Without having a clue what's going on with the stairs.. or the ceilings.. or the surrounding spaces... or the room measurements...

(unlabled = office, and door to office could move to new "hallway"; closet door could go through the bathroom or the bedroom, depending on your preference)