nothing wrong with sleeping outdoors, and the benefits are many. you can also get a lot of benefit from just a few minutes of walking barefoot on earth.
not sure i would buy an expensive grounding mat. all you need to do is drive a metal stake into the ground or run a metal cable to your cold water pipe and touch that every so often to discharge.
tai chi or chi qong done barefoot outside is even better.
i am sure that these grounding issues have a lot to do with heavy metal toxicity which are making a giant mess of people's nervous systems.