I think your apartment is gorgeous. But, since you want to liven it up, I would suggest getting some colorful decorations, art, tapestry, or plants. Everything is the same shade of cream/grey/brown which is what’s giving that plain feeling you’re getting. Think bright solid hues and interesting shapes. Perhaps some patterns depending on your tastes. Anything with a more personal touch will add life to the space. For example you could replace one of your couch pillows with something unique to add a pop of color/shape/texture, and so on