I have just finished the en-suite and SWMBO would like the floor tiled. I
have tiled many a wall but never a floor and would like a bit of
advice/opinions please.

The house is a modern build (1992) and the floor is made from those large
boards that are a type of chipboard, not the normal Conti type but made up
from large pieces of wood chippings, and has a slight Orangey tint to, it
sorry don't know the correct term for them. The guys in the tile warehouse
say I cannot tile to this as it will "suck out the moisture from the
adhesive and the tiles will eventually pop off!"

Apart from the obvious of making sure the floor is 'solid' what preparation
do I need to do on this type of floor? Can I not just seal it with a
PVA/water mix (what ratio)? The tile guys say to cover in plywood and tile
onto that. The thinnest ply I have seen is 4mm. If I go this way then the
floor would end up approx 3/4" higher than the bedroom, the door opens into
the bedroom so this doesn't cause a problem with that, but what is the best
way of dealing with the 'step' from an aesthetics point of view?

Many thanks

John