I totally agree with llrn7470.
The "Automatic" heating pads (I believe made by Sunbeam),

Get a dual sided control, bottom heating one. (mattress cover). If you get a single control, your spouse will have a fit, (not to be blamed on them). But, especially more important, I found, If you buy one that's 10/$20 cheaper and it's a Blanket (lays on top), you'll get over heated, and throw it off in the middle of the night, and start the whole cycle over again.

Being a Master Plumber, I understand how (this is more an electricians thing) the "Automatic" part works. There is a wrapping around all the heating wires in the blanket.
The "cooler" they get, the more resistance, and the more heat they'll give off. (Yur cold spots, your Feets, arms, like that.) You couldn't feel any more like a bug in a rug!
I had a few of these automatics, til wifey decided she needed them more...
Believe me, they're AWESOME!
I'd NEVER buy a regular electric blanket again!
These are completely washable too!