You can set exterior-grade bender-boards vertically in your preferred pattern, holding the curves in place with narrow pointed pieces of wood. Once you have made your adjustments and the support pieces are firmly in place, spray the area with weed-blocker and fill the areas with a couple layers of weed cloth (you can get a big roll at COSTCO or Home Depot) to suppress growth of weeds or grass. Then place your stepping stones and fill the area with your selected colors of gravel or mid-size crushed rock. It is time-consuming, but the preparation is worth the time.

In this case basic black plastic landscape edging was used.