Next year I am making coloured photocopies. It casts a soft glow. Many times I turn off the overhead lights and the light from the windows and my desk lamp creates a nice atmosphere. I also have a small cd player near my desk. I also have an 5x8 ft carpet in a corner for lounging and reading.
Plants are always a nice addition.
You could get a fake fig tree and string it with small white Christmas lights. Make it a place that makes YOU feel cozy and so will your students. My room is decorated much like you described. It's fun to hang decorations on it for diff. I also have a small lamp on the corner of my desk.