This is not what you’re asking for so I hope someone else replies, but I got a heated mattress pad that has 5 different heating setting and can stay on all night and it’s not great for summer time obviously cause it gets very hot but omg my favorite is having it on and my whole bed anywhere I turn is just heated, it feels so good on my lower back and I wouldn’t have thought of putting a heating pad there necessarily and I turn on my tummy and let it just absorb all the heat. I also think heated blanket is a magnificent idea. Just throwing this idea out there too cause when I was considering which large heated item to get I was nervous I would forget to turn off the blanket and it would be a fire hazard or something even though I know maybe that’s a tiny bit of a myth?, and I wanted to be able to keep it on all night so I wouldn’t wake up in pain and want the heat again, and I wouldn’t feel as comfortable leaving a heated blanket on that long. But, heated blankets are more mobile and I see all the benefits of them too. Sorry so much unsolicited advice!! This is the mattress pad I have, it’s a bit expensive but I wanted one that was mainly cotton instead of polyester: https://www.amazon.com/Holmes-Premium-Quilted-Electric-Mattress/dp/B075ZVCZ8M. Also, I have fibromyalgia too, so maybe my desire to have fulllll body heating pad all night is more helpful for fibro and a blanket would be more helpful for targeted areas of endo, idk.