This is a great room and I love the staircase, but do you want 2 of them? Mirrors can be tricky to decorate with. They need to be places where they serve a purpose like reflecting gorgous light from a window or a lamp, or a beautiful view. The mirror in the position you will have it will be like hanging a picture of a staircase. What about moving the sofa to the wall with the mirror (location), placing 2 chairs with the end table in between them in front of the window, and hanging drapes far outside the window to make the window appear larger (don't have them cover the window and hang them close to the ceiling) and put a great lamp on the table. At the side of the sofa (if it fits) put the other side table (closest to the hall) and hang the mirror vertically behind the end table also with a great lamp. The coffee table can go in front of the sofa with minimal accents. You can put a couple of small ottomans grouped together on the staircase wall for additional seating. The aquarium is a little distracting, maybe not the fish, but the aquarium and stand are; maybe you can find a better alternative or move it altogether. You need a little color for interest in the form of throws, pillows and art. A palm tree (real not fake) in the corner (where you have the fish tank) with an uplight will create interesting shadows at night and a natural element during the day. It looks like you have a bluish green color going on in the other room, maybe you can play off of that color to find accent colors to make the house flow. Repeat the same accent colors in both spaces or relate them somehow. By the way, you have a beautiful ceiling, play up that ceiling and draw the eye upward, a ceiling is a 5th wall. This would be a great place for an accent color or a metalic. The mirror and the palm and the drapes (because they are verticle) will help draw the eye up to this fabulous feature. Good luck.
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A lot what He. She said I was thinking the same thing. Even another idea I will have to put it together little more.
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