Here are your answers, the Durock and Wonder board are both cementatious type underlayments and the hardi backer is a gypsum base underlayment. There also is a new version by Durock called Fiberock. Here is a list of the sizes.
Durock cementatious 5/16 & 1/2
Durock fiberock 1/4, 3/8, 1/2
Wonderboard 1/4 & 1/2
These sizes are to my knowledge
The 1/4 should be good for the floor as long as you get the soft spots out of the floor first, and the 3/8 or 1/2 should be good depending on the thickness of the remaining drywall. The hardi backer and fiberock are more ridged and better for the walls in my opinion and the cementatious for the floor.