Sleeping mats? Again I have one. Is this an unnecessary luxury?
Its a personal thing - a good night sleep cannot be overated.
If you are happy sleeping on the ground and don't suffer then do it.
If you wake up stiff and aching shoulders and hips (particularly if you are a side-sleeper) use a mat.
A mat will not only make 'the bed softer' but will also give insulation from the cold ground (not that, that's a problem at the moment)
I would suggest that most DO use a mat of some sort.