prom/formal dress

i have a strict mum. every dress ive showed her for prom/formal she has said no, becasue u can see to much of my boobs, to much back, to much shoulder or to high split. so please help give me som good websites where only a little bit is shown. bc i dontwanna be looking like i’m formthe 70’s but i also want my mum to approve of my dress. pls some websites or dresses <3