Before you toss out your old store brand stuff, consider making your coffee using a cold brew method. Cold brew is less acidic and pulls fewer compounds from the beans. This less acidic brew will have a more chocolatey, sweeter taste. By weight, you want about 1 part grounds to 9 parts water (that's 100 grams of grounds to 900 grams of water). Then, if you want to make the brew more like traditional drip coffee, you'll want to add some additional water when you serve the coffee (typically ice). Cold brew doesn't necessarily mean iced coffee, though.
Just a side note about acidity, you can buffer that acid by eating breakfast. Carbs, fats, and protein can help with some of that intestinal rumbling one might experience when drinking coffee on an empty stomach.
If you still find that coffee is giving you problems, you might want to look into a local roaster. In my city we have a handful and the freshness of this kind of coffee is off the chain.
If that option is too pricey (it may be) Eight 'O'clock sells a Colombian that is really nice and at a fair price if you buy it in a larger bag. You'll want to store most of it in the freezer and keep the stuff you're going you use for the week out if you're concerned about flavor loss (you might not notice though, that's coffee nerd shit tbh).
Can't attest to flavoring because I'm too much of a snob.