@Lanzastar If you are car camping then you can take anything you want...there are all kinds of cots and mattresses.
For backpacking, 20 inch wide pads are the norm and many lightweight two person tents are tapered towards the foot end such that when used by the nominal occupancy only 20 inch pads will not overlap at the foot end. If you are primarily a back sleeper or of a larger persuasion you will probably prefer a wider pad to keep your elbows off the ground. The pad I like is the Thermarest X-lite Regular Wide or the Large if you are taller. These pads are nominally ~25 inches at the shoulders and taper towards the feet. I don't know if two will fit but you can probably fit one if the other is a 20 inch pad in a typical UL2 type tent. I actually have an X-lite Regular which works fine for me because I am generally a side sleeper.
It really it comes down to what you need to get you a good nights sleep.