Had similar stomach irritation from pounding Americanos. Switching to cold brew and adding milk helped. I use a cheap handheld Aerolatte at work, and a Nespresso Aeroccino at home to heat/foam fast.
Easing into vegetarian worked for me: swapped lunch meats for hummus or tofu, kept eggs and yogurt at first. Low acid choices like oat milk, chamomile tea, and plain rice were gentler.
If caffeine feels more like a habit spiral, I’ve been looking into Abbeycare for guidance on cutting back without going extreme. Nice to speak with someone when self limits keep slipping.