custom castor oil pack made of jersey knit conforms easily to your body, open on both sides so heating pad cord can go to either side. Sew 3" elastic ace bandages with velcro to it. You might still have to reinforce the velcro with a safety pin so you don't unravel. On opposite side of the body, you can do hot/cold therapy.

shown with: shirt on and another elastic ace bandage on outside of shirt. when packs are too hot or too cold, this can hold it to the outside of your shirt. As it cools, you can move it to the inside of your shirt, wrapped in those ace bandages.