I'm not sure how healthy or unhealthy diet sodas are, I'm allergic to the artificial sweeteners and drink the classic full sugar versions.
But friends with GERD say that they felt a lot better after ditching the caffeine and stopping diet drinks with artificial sweeteners.
They tended to go for caffeine-free herbal teas, homemade dairy free smoothies, fruit juices and coconut water.
The three most popular teas were chamomile, ginger and licorice.
Good luck!