“Living In High Cotton”
Anyone familiar with history of the United States knows how much the South depended on cotton fields for its economy. Saying that someone is living in high cotton means that they’re financially secure, that is to say, wealthy.
“Hush Your Mouth”
This might not need much of an explanation, but it’s pretty uncommon to hear someone outside of the south tell someone to hush their mouth. It is a way to say to be quiet, as is saying to “put a sock in it” or “close your lips.”