I tried the chillow, it works okay, you have to fill the chillow with water to get it to work. The part of the chillow where you rest your head does start to heat up due to you natural body temperature, but you simply move your head to find a cool spot again. They are a bit heavy once they are filled with water, you can slip them under your pillowcase if you want to, but they make your pillows go a bit flat. If you are relying on coolness to help a migraine, then it could help, but be aware it is not 100% perfect.
The company that sell the chillow also offers a mattress cooling pad.
Stay away from this though, it is contains a cooling gel within the pad, that is wonderful when you get in the bed, but your body temp heats it up during the night and the gel retains the heat, unlike the chillow. It felt as though we were waking up on an electric blanket, most uncomfortable!!
Hope this helps
Sue