Cement board or drywall? - Searching for green alternatives

I thought that designing a green bathroom would be easy. All I had to worry about was to pick out the tiles, low flush toilet, bathtub.... Well, it turns out that it is not that simple. Just replacing the drywall in the bathroom creates a big green dilemma for us.  There are a lot of products with a lot of different ingredients and to try and find one that is non-toxic, made by a reputable company and does not have a misleading name is very difficult.  

Our contractor suggested using cement board around the shower area and green drywall in the rest of the bathroom. Our problem is that green drywall is not really "green".  It has toxic chemicals in it to prevent mold and fungus growth and is only called green because of its colour; not its sustainable qualities. We are not comfortable using it for our bathroom. 

During my search for a drywall alternative for bathrooms I came across DensArmor gypsum wall board made with fiberglass mats on both sides. It is  naturally water/mold resistant and recommended for wet/humid areas. I thought that I had found a solution until I learned that it is made by Georgia-Pacific Gypsum, which has been fighting law suites for manufacturing toxic drywall. At this point I don't trust them so DensArmor is out.

We are still searching for drywall alternatives, but leaning towards using cement board instead of green drywall. Cement board is water resistant and used in areas where there is direct contact with water. It is also used as a tile backer. 

Cement board 

We will need to apply a drywall compound on the cement board to finish it off and to make it smooth and ready for paint. It will be more work, more sanding and more money than using drywall, but worth the effort for us. Our contractor doesn’t know about our plan yet but hopefully he will be on board.

Mia