I have a workshop floor that is 4" concrete on a DPM on hardcore/soil.
The plan is to put a wooden floor in to make it more comfortable to stand on
for long periods.
I don't want to lose too much ceiling height so i was planning to put tiling
batten (25mm) down as mini joists with mortar under to adjust the levels and
18mm ply as the floor surface.

Is it worth putting insulation underneath eg 25mm polystyrene or as the
space under is not ventilated, would the static air gap underneath be
virtually as good as the insulation?

The area is 30 sq metres so I don't want to waste money on polystyrene
unless it is going to make a useful difference.

The walls and roof will be insulated for comfort in both Summer and Winter.
Depending on how cold it gets and how much I use it in Winter there will be
some form of space heating at least to the level to prevent icicles forming
on my nose!!

TIA

Bob