Another option for the mirror would be to make one using the same fluted molding & bulls-eye corners you have around the windows except buy white & do a tea stain on it or if you are timid about that then simply paint it a cream/tan color like your towel bar. If you don't own a saw the cuts needed could be made at the big box store where the trim is purchased for a small fee. Yet, another option would be to repeat the curve seen in your sink, by using a brushed stainless colored mirror in an oval shape. Just food for thought.

I think you should consider having a mirror made to match the window trim and color. I'm not too crazy about the geometric bath mat/rugs. Would look for something equally as elegant as the rest of the bath and the lovely shower curtain.