I've been playing around with something similar. I am curious how much benefit adding in a sanctuary or a purify would be. Each of them directly counters a few fgs. In my experience, purify isnt worth it because the gods that use poison are beatable without it, using this type of deck. That may have changed with the implication of new fg's that use poison. Sanctuary is kind of in the same boat. Sanctuary takes down decay and dark matter, and gives you a chance against dream catcher.
Overall, my recommendation would be either +1 sanctuary, or -1SOG, +1sanctuary.