Catholic teaching on sex and marriage is beautifully, systematically and definitively set down in Pope John Pau;'s encyclical the Gospel of Life and his work the Theology of the Body, a compilationof his summary of that teaching. The easiest book for beginner is just that, Theology of the Body for Beginners by Christopher West. Good News about Sex and Marriage helps couples apply that teaching to their own marriage.
Anything that promotes and perfects the conjugal union of the married couple and leads them to the bodily expression of their love that is open to life and to God’s will for them is okay.
There is absolutely no role for any sexual expression, activity, or behaviors that mimic, arouse, or allude to sexual activity outside lawful marriage. Any sexual activity or expression in marriage that results from one spouse reducing the other to an object of sexual pleasure rather than embracing and respecting their full dignity as a person is wrong.