One of the central practices of the Mussar movement is studying and meditating on classical Musar literature. Here is a list of current and classical books. All are available on Amazon or at Feldheim Publishers
Books by Alan Morinis
Climbing Jacob’s Ladder
Every Day, Holy Day
With Heart in Mind
Mussar Classics
The Duties of the Heart, by Bahya ibn Pakuda
Gates of Repentance, by Rabbeinu Yonah
Orchos Tzadikim, anonymous
Mesillat Yesharim, by Rabbi Moshe Chaim Luzzatto
Cheshbon ha-Nefesh, by Rabbi Menahem Mendel Leffin
Strive for Truth, by Rabbi Eliyahu Dessler