Depending on how they’re roasted and brewed, decaf coffee beans can still have some level of acidity. That said, decaffeinated beans are often better for people who are sensitive to acids, mainly because the human stomach generates more acid when caffeine is present.
If you want a decaf coffee that is best for sensitive stomachs and acid reflux, go with beans that have been decaffeinated using the mountain water process; this is the most effective for removing caffeine without the use of harsh chemicals so it’s the most gentle coffee for digestion.