Also choose a pot size based on the root mass, not the plant size. The roots should fit comfortably. If they aren't touch the sides of the pot, then the pot is too big. But they shouldn't be squished in either.
Sometimes one size is a bit too small, and the next one slightly too large. If the plant has thick roots, I'd err up a size, but use potting medium to push the roots out to the sides of the pot. If their thin, fine roots, err down a size.
Don't pack the medium too tightly. With bark that's hard to do, but with moss, keep it quite loose to allow sufficient air pockets.
What types of plants are you looking for. List some genera. Most growers tend to specialize.