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Do you even need a mat? Finding soft ground or just being tired has worked for me, I assume I have a little more "natural padding" than someone like @skinny though...
Josh Ibbet mentioned using his shoes as a pillow and it being comfortable, I've tried it (and sleeping with my head on the edge of a 29er tyre/wheel), couldn't move my neck the next day time, the tyre was equally uncomfortable. No silver bullet with these things...
I've got one of these. Welcome to try it out.
If you can sleep on your back, it'll be fine.