Don't do the walls. I agree with other post that the room is already very busy. There is a geometric harshness that needs some softening. I like the idea of a sitting area at the top of the stairs. When you enter the room the eye is naturally drawn to the window area. Some drapes, floor to ceiling, in a light, sheer material would add softness. I would layer an area rug on the platform, and find some nice fabric chairs, even a chaise longue, and an "out of the box" coffee table. Perhaps an old trunk or ottoman. I would place the bed on the lower part. The bedding should coordinate with the fabrics on the sitting area.
If you truly wanted to keep the bed at the top of the platform, you need to change the direction of the bed. It's better feng shui to walk into a room and have the bed face you. So place the head of the bed at the windows, and frame the windows with some soft billowy curtains. I would layer an area rug on at the bottom level of the bedroom, and place some chairs and a sofe, or chaise, there. You could place the sofa along the wall and have the chairs face the sofa, angled.
You have too many elements up against the walls. Bring some of those away from the way and you will find that the room becomes more enveloping.
Good luck!