You have to make the decoration and furniture balance in both sides of your Japanese living room. Balance does not mean the exact size and placing but the balance here means the balance of your mind when you enter the room. You may make it difference but make sure that it is not too crowded. If it is crowded, the simplicity soul will disappear.
The decoration should be made from natural elements such as wicker, bamboo, rice paper, and stone. Make it, again, simple. Never add any complicated sculpture or artwork. You can add some Japanese wallpaper design to make it feels more like Japanese living room