Which tile backer for a stand in shower bath?

[Simplez]

Its a fairly small bathroom - 2.5m x 2m with an outside window. Will be having a straight bath, WC and toilet fitted.

Will be having an external thermostatic shower mixer tap - not running behind the plaster in the wall.

So what type of plasterboard / tile backing should I use for the bath area and behind the sink.

Also it will be tiled - so should I use standard grout or something else?

Currently the bath is stripped back to the walls.

 

[footprints]

Hardiebacker or any similar will be fine, if you want to improve insulation (say on an outside wall) marmox board is good.
Avoid standard plasterboard.