My Dr. advises a heating pad on low is fine and not for long periods of time.
As far as stretchs go - I stretch every morning while laying in bed and it has made a HUGE difference in how my back feels. Here are a few that I do:
1) Butterfly stretch while laying flat on my back instead and tucking my chin towards my chest. Do this 2-3 times.
2) laying flat on your back, legs straight,
now bring both legs toward you bending the knees. Now
grab those knees with you hands and pull them as far forward toward you
as you can. Hold for a few seconds, let the legs back down to straight
again, slowly. Do this 2-3 times. Again tuck your chin to stretch deeper.
3) laying flat on your back lift your but up and hold for several seconds. Do this 2-3 times.
Finally I sit up
4) and stretch my arms and neck... these have worked wonders for me. GL!
ETA: I just started doing #2 above along with arm and neck stretches before bed too so no idea if it helps much or not... but worth a try :)