Not sure how far you've gotten with your project, but we've been a fan of using Plant Select program plants since we've started doing our yard last year. Part of the reason we like it is that it's a partnership program between Colorado State University and Denver Botanic Gardens to find plants that do well in CO mostly with little water or maintenance. Ideally, they should have less vested interest in trying to "sell" you something. If you go to their site, you can go to the "Find a Plant" section and filter to find plants you want. I'd suggest looking mostly at the Petites and Groundcovers. Although there might be some listed in the Perennials category that have small features good for a fairy garden as well.
