First Time Tiler - HardieBacker?

[HandyManDan]

After I finish the ceiling off in the bathroom, chip the rest of the tiles of from the walls, finish the walls, and stain the cladding going around the bathroom, I'm going to get to the Floor, have been reading up and don't fancy running into broken tiles at a later date, I'm pretty sure the tiles soon to be on the wall will be fine just sitting on the plasterboard because the ones already up have held up fine, no problems, however, the floor is solid oak wood at the moment, and you can see the wear and tear were the wood has had the most amounts of water present over the years.

So that brings me to HardieBacker, haven't seen a great deal on these cement boards, just a lot of people in the youtube vids just tiling over ply. Future proof would be ideal, but is hardiebecker really needed?

Do I really need to install it the correct way according to Hardiebecker...First ripe up the old floor which brings you to the floor panels take that up and add noggins between the joists, lay the panels back down, apply min 15 mm ply then put the hardiebecker on top. Was considering the 250 6mm, but is this really needed. Was thinking about just installing the Hardiebecker over the floor panels, without the ply as that wouldn't bring the floor up as much. With 15mm -18mm ply below that would just make the floor to high, the bathroom is only small it's only at the most 2 by 3 M.

What do you guys think, leave out the ply, go with the Hardiebecker, leave out the Hardiebecker, go with the ply, scrub clean the floor panels, and put a few extra noggins between the joists then just tile?

cheers

HMD