I'm not sure why you're concerned about low acid coffee...the acid in your stomach is greatly more times what coffee you're putting in there. It's not the acid in our stomach that's causing our UC.
Drink coffee if you don't mind the 1-2 hour's worth of colon stimulation it usually causes...you know, provoking a bm.
Herbal teas won't take you out of a flare but some are supposed to be calming (I never really noticed this effect but some taste pleasant and are warming to drink at night without having the caffeine you may not want at night).