I found a heatingpad at Walgreens which is nice. I’m used to riceheaters, and I’ve been happy with them, but the Thermipaq s better. It contains some kind of clay, and it heats in the micro. It’s slimmer and lighter than the riceheater. It also has a velcrostrap, which means that you can wear it around your package while walking around.
It keeps getting a little warmer after the heating, so don’t get burned. I don’t remember the price, but it wasn’t too expensive as I recall.