Floor prep advice please

[danc07]

Hi all I am at last stage of my bathroom refurb (the floor) and would like advice please,floor size is 1.7mx1.8m,existing is floorboards which are not to bad but the floor has a fall of roughly 15-20mm,don't seem to be much movement not a very big area.
The mrs (the boss) has chosen 600x600 polished porcelain.
I am in the building trade (don't shout) so have some knowledge,my prob is there is so many ways to do this I believe,the 1 way which I really don't want to do is rip floorboards up would be a nightmare.So any suggestions tips tricks will be a great help.Oh and my thoughts are PLY and HARDIBACKER
THANKS DAN.

 

[Del W]

Screw boards down so theres no movement.Hardibacker 6mm glued & screwed.Self level where required.Tile.

 

[danc07]

Thanks del w