Underfloor heating - options

[cpmarvin]

hello,

I'm looking to add underfloor heating to downstairs in a terraced house. The aim is to re-use the laminate and underlay , but trying to understand the various options for dry screed installation.

Actual:
- floor boards ( 22mm)
- underlay (3mm)
- laminate (12mm)
Total: 37mm

Option1 - diffuser plates
- on top of joist diffuser plates ( 0mm)
- cement board GIFA FHB (18mm)
- underlay ( 3mm)
- laminate engineered flooring ( 16mm)
Total : 37

Option2 - diffuser plates ( currently preferred option)
- on top of joist diffuser plates ( 0mm)
- cement board GIFA FHB ( 25mm)
- laminate ( 12mm)
Total : 37mm

Option3 - diffuser plates
- on top of joist diffuser plates ( 0mm)
- cement board GIFA FHB ( 25mm)
- underlay ( 3mm)
- laminate ( 10mm)
Total : 38mm

To get the exact height ( no doors/skirting modification) , i would either have:
Option 1 - change laminate to 16mm
Option 2 - remove underlay
Opition 3 - change laminate to 10mm

I prefer to remove the underlay , but not sure i can do that.
The Laminate increase to 16mm or decrease to 10mm does involve an extra cost ... So boils down to the question , can i install laminate flooring without an underlay ontop of cemeant boards ?

Thx in advance.