A while back, while searching for the armor padding, I had discovered that this version actually exists, and set out to find one in the wild.
It was a pain to actually find it, but eventually (and just recently) this arrived...

This is the same original vintage Dutch military sleeping mat.... only factory made in 8mm thickness.
Meaning, it is the correct thickness with no slicing needed.
Just cut to shape and glue.
Only one side has the squares, with the other being a flat surface.

16mm on the left.
8mm on the right.

Wow that’s amazing, great find!