Any inexpensive heating pad will work, but there are some things to look out for. Use a few Velcro adhesive dots to keep the pad from moving around on your desk. You will probably need to put a piece of stiff cardboard over the pad since most mice need a very flat surface. Choose a pad that allows you to conveniently adjust the heat. Cover the mouse and your hand with a towel, but be aware that its easy to let the mouse get too warm. Look for a pad with "auto-shutoff". A cheap mouse may stop working if it gets too hot, but let it cool down and it should start working again in a few minutes. My shop is typically about 55 deg F in the winter but this makes it very comfortable to use a mouse. I've done this for many years and never killed a mouse.