White Sugar is sucrose which is a disaccharide (double-sugar). The duodenum also breaks down starches into another disaccharide, maltose. Then the remaining small intestine releases enzymes which split disaccharides into monosaccharides like glucose and fructose. Finally monosaccharides are transported from the intestinal wall into the bloodstream. Meanwhile candida feeds on disaccharides, particularly if they're easy to get at, i.e. in a liquid.
Coffee is also a laxative which means it helps liquidise food already in the intestinal tract, so you can see why sugared coffee can cause problems.
The sugars in honey are already monosaccharides and easier to digest, so you could try it (raw manuka if you can afford the price) in place of sugar. You can also buy fructose syrup, but there are concerns about its health effects.
Do not use artificial sweetners. This includes "natural" sweeteners like stevia, which is a steroid.