When using gray paint, I would suggest using a flat finish, not a semi gloss because it can sometimes look too industrial if there is too much of a shine.
Another trick of the trade is bringing in a lot of different kinds of light sources such as table lamps, ceiling fixtures, and sconces. These fixtures give your space warmth and versatility because of all the lighting options.
I like to use pops of color with gray, especially with accessories that you can change out throughout the year.
Thing about using a wallpaper instead of paint for a textured look.