Assuming the door is a standard 6'-8" height and a roughly 3'-0" wide landing at the top of the stair, there shouldn't be any problem manuevering anything, even a king size mattress.

If you are concerned try moving the box spring in I usually have 2 box springs for a king and the mattress folds . The dressers could be an issue but if not longer than the doorway is tall still not an issue .

I have almost this exact same situation with one of my upstairs bedrooms--don't know how wide your hall is--my hall is only 36" wide. (And I have a long open hall without a door like you have at the top of the stairs...assuming that door will be removed?) You won't have any problem getting a mattress or dressers in there. The dressers can go in 'on end' if they are too long to turn the corner.

However, there was no way the wing back chair would go in. So if you are thinking of using larger pieces of soft furnishings like chairs, a loveseat, etc., you will probably have to find a Plan B. Going through the window was the only way I could have gotten that chair into the room...second floor?..nah, not worth it so I scuttled the idea.