It is necessary for me to remain in contact with my former spouse. How should I dress in front of him?

A woman is required to cover her body with the exception of her face and her hands in front of all men except of her husband and close relatives to whom she may not be married.
Her former husband is just like any other man. Since a woman and her former husband have to discuss certain matters relating to the upbringing of their children, they may meet in the presence of either the woman’s new husband or some of her immediate relatives. She can wear the same type of clothes she wears when she goes out. In other words, she need not cover her face and hands.
And God Almighty knows best.