Hi Jody, I changed the title of this thread - this is not an idiotic question, it's a very important question. I've done quite a lot of trial and error with various kinds of "dirt", and gotten some good suggestions from other people along the way.
2 good things about "real dirt", compared to pure coco fiber, is that it is less likely to stick to amphibian skin, and it has some properties that help it to break down waste products. It rarely molds.
I use a 50/50 mix of top soil (bought in a bag at walmart) and coco fiber. The advantage of including coco is that it holds moisture better than most kinds of dirt do. I also mix in some fir bark chips or cypress mulch if I have it around.
If you are having problems with coco fiber being too dry, I think you need to add more water to it (POUR some water onto it) - either that or else you have too thin of a layer of it. Usually, cocofiber holds moisture pretty well.