That stair side wall is pretty busy with doors, angles and recesses; no need to add anything there. IMO, the solution to add texture to your room is with rugs and pillows. A change of wall color, interesting art and some lamps will give a more cozy feeling and are better solutions.

You could simply add vertical batten strips to the walls for texture. IMO it's a classic timeless solution.

start with an area rug under the sectional, some drapes on the windows and mount the TV on the wall.

You could do some contemporary style moldings or wallpaper. I would only do the TV wall