I'd use a small tent in combination with a tarp over the front door. A tarp is always useful to take with you anyway (might even be just your poncho).
As for sleeping mat, I use a regular foam mat. It's good enough for me, I just put some sweater under my head and something under my lower back and something under my feet to give me comfort... In an old scouts book I read they dig out pits for the shoulders and for the bottom to make it more comfortable. Though that was perhaps before they used floors in tents..
That Z-rest from thermarest definately looks good kit, might get one myself...
I see to often punctured sleeping mats that I don't want them, though I guess with care you can avoid it...