A one-room space feels messy to people when everything is mixed together with no order. The fastest way to fix that is to “separate” the room without building a wall. You can separate spaces using a rug, the position of your bed, and one simple divider like a curtain, a bookshelf, or a screen. Your bed should not be in the center of the room if you can avoid it, because the bed is the biggest item and it controls the look of the whole space. Put the bed against the longest wall and keep a clear walking line so the room feels open. Then choose one corner for a small work table or a small chair so you have a “day area.” Even if the room is small, having one corner that is not bed-related makes the whole room feel more adult, more organized, and more beautiful.
Simple example: Put a small rug beside the bed to create a “sleep zone,” then place a small table and chair on the other side of the room to create a “work zone,” and keep your storage in one wall line so the room looks tidy.