I think monochromatic is sophisticated looking. Just add lots of texture and sparkle for interest. Monochromatic doesn't mean colorless. Type in "monochromatic living room" in Houzz search photos and you'll see lots of lovely, sophisticated spaces with color.

A way to think about that monochromatic ideal is to consider a spectrum of colors like a black and white photo with all the shades of gray and silver accents, but you can also do it in a warm way like a sepia photograph that runs from chocolate up to cream with shades of camel and metals in oil rubbed bronze. This would vary depending on your preferences, the color of your white walls (warm or cool) and the color of your existing pieces.

How much natural light do you have? What colors do you have now in upholstery that you need to live with for awhile?

All colors can be sophisticated if done properly, but the trick is to get a very muted shade or even a dark drama tone, especially in public rooms. Since you have dark floors, you will need to add more lighting than most.