I think if you install mirrors, you will double the lighting you already have in the room. Put 4 of the same type mirrors together to give the idea of a window.
If you have to keep the treadmill and couch in there, maybe move the couch forward enough to put the treadmill behind it. Then put your sewing table (short side) against the wall by that 9 pane door so you aren't looking at the couch/treadmill. Does that make sense? Any how, hope this gives you some ideas. (Love the color of the walls by the way)