A combined stretch and exercise that I like is a variation on the above. So lie on your back bring your knees up to your chest and wrap your arms around them, then also curl up your neck. It does really stretch your spine. The variation is then to rock from side to side and back and forth.
With my back pain a couple of people have said just to pull one knee to my chest at a time and hold that - all while lying on the floor. Then alternate with the other knee.
L4-L5 Herniated disc, L3-L4 mild bulge, L5-S1 Spondylolysis