@Shop-et-al I got gel pads (various sizes and shapes) from Amazon. The problem with them is you have to heat them in increments of 15 secs or they pop. The sock filled with rice eventually starts smelling and then you need to replace it. I had an incident when the sock got overheated, had a hole and the rice got straight into my eyes. The only thing that works for me is the heat pad with a cord. I can put it on my pillow, lie down or sit up and it swtiches off even when I fall asleep on that after some time. Works for a bad migraine, neck pain coupled with an Excedrin.
I would so want something invented like you said, though!