We'd like to update our "yellow" walls with "green" posts in our basement. We have medium grey carpet which will stay. We are also keeping the sectional, but would like to find a slip cover to update its look, and replace the window treatments. We'd like a 'warm' cozy look, but not sure what color would work best. My first thought was grey walls, but I don't want the room to look cold & too matchy. Please Help!