It is always interesting when a question brings a new product to the table.
Such is the case with DragonBoard for me. From what is presented on their website, I would say that this product would suit your specification perfectly.
DragonBoard is composed of:
- magnesium oxide,
- magnesium chloride,
- water and
- a fibrous material (presumably to hold it together), and
- does not contain any organic solvents, asbestos, oils or toxic components, or any heavy-metal salts.
The board itself will not provide nutrients for mold as well as:
- provides a fire rating that meets or exceeds that of drywall,
- is completely waterproof, and
- can be finished with typical drywall finishing techniques and materials.
The last part is probably the subject of your next investigation, and I would recommend using a hypoallergenic drywall compound for finishing.
Best of luck on your project!
For more information:
Read "Is there such a thing as green drywall? If so, what alternatives to conventional drywall do you recommend?" a Q&A answered by Mary Cordaro.