Do you know that you already have a natural corset in your body? Your transverse abdominal muscles are your natural corset.
If you feel that your transverse abdominal muscles are tight like an armored warrior, please try the triangle pose in Hatha Yoga. This pose helps your backbone release from gravity, so your transverse abdominal muscles will also release from being an armored warrior. You will feel longer than before between the pelvis and the rib cage.
If you want to have good posture, please use your natural corset. This also helps to decrease lower back pain.