Hi there,
we could offer you our Ultraslim system which is only 18mm thick (same as 20p coin).
Heavy boards are made from recycled gypsum, paper and water, mixed in an 80%- 20% ratio to produce homogeneous, dense sheet material that is cured, they are pre grooved for 12mm pipe which will be spaced at 150mm.
Engineered wood (floating floor) and tiles can be laid directly on top.
Parquet (if glued down to the surface) and carpet would require 6-9mm plywood or chipboard overboarding.
It's a very quick installation method, boards can be fixed by low expansion fixing foam (which we also supply) which dries in 1hour.
If you would require some more details or would like me to do a quote for you please feel free to contact me and I'll be happy to help.