A great way to relax the muscles of the back and sides and to gently stretch the muscles between the ribs to enhance your breathing.
WARNING: Seek advice if you have disc or sacroiliac problems.
You'll need a bolster or a stack of firm pillows. Sit with your right hip against the end of the bolster, lengthen your spine and rotate towards the bolster. Put your hands either side of the bolster and "walk" yourself down until you are lying along its length. Turn your head to whichever side feels most comfortable. As you relax the upper back allow each soft exhale to settle you further into the rotation and into the surface of the bolster. To come out, use your hands to support you just as you did on the way in. Repeat on the other side, enjoy and let me know how it felt.