I bought this one for my neck. It really helps with my neck pain and it heats up really fast. The on switch has to be held down for it to work which sounds like a pain in the ass but I just put it under my leg or use my knee to keep the button held down
Battle Creek Thermophore Classic 4 x 17 Inch https://www.amazon.com/dp/B000ZHNKP0/ref=cm_sw_r_cp_api_luYYzbQXHPFTX