If you talk to your friend, you can say like these: 너의 엄마, 너의 어머님,니 엄마, 니 어머님, 너네 엄마, 너네 어머님. if you talk to olders than you, you should say like these: 모친, 어머님. If you talk to someone among people, you'd better to say like "his name or her name 씨 어머님" You have many options so it can be easy.