At the craft store, you can buy "waste canvas". You machine baste it on most any fabric you wish to cross stitch on. It is an open weave, with a colored thread every 10" so you can keep track of your count. You do your cross stitch design over both this canvas and your garment. Then you wet the garment and the waste canvas sort of just comes apart and you pull it out thread by thread. Voila!

What you describe is called "heirloom sewing". If you do a web search for those two words, you will find lots of sources for the fabrics, classes and books tp get started making such clothing. If you are lucky, maybe someone will sell the basic unadorned dresses for your artistry.

Also, I don't know about those particular dresses, but Michael's, a craft store in our area, sells aprons, bags, shirts, etc. for adding your handiwork to.