Bathroom backer boards

[MickFussey3]

Hi I am about to under go the job of tiling my bathroom floor and walls .I only have a maximum thickness after I have removed the floorboards of 22MM. Can I lay Hardie or any other 12mm tile backer directly to the joists which are 24mm apart without ply as the tile I want to use is 10mm.
If i can this would be the perfet measurement
Mick

 

[MickFussey3]

Thanks I will go for 15mm sound better Mick