You may have already thought this, but sheet rock isn't a great product to have in our homes. If it gets wet, it's ruined - or it's mold food. Plus it's not breathable, it's filled with toxins, and about half of the gypsum that is being used in sheetrock (drywall) is synthetic gypsum, using a process called FGD, which can offgass vapors well after it's installed.
MgO board is an amazing alternative. It's been around for thousands of years, and the Chinese have been using it since they built the Great Wall. Wikipedia has a fascinating history of the use of MgO, which you can find here: