Petticoats are pretty much the most fun clothing item ever: they’re fairly cheap, easy to put on, and they totally change an outfit. The kind of petticoat you need depends on a few factors:
What are you wearing over the petticoat (if anything)?
If you’re not planning to put a skirt over it, don’t hesitate to get a pretty, colorful one. For additional color and fullness you can also wear one petticoat on top of another one. Did I just blow your mind?
Do you want the petticoat seen?
In certain eras, it would be a breach of etiquette for your undergarment to be show. Fortunately we live in an era where we can show as much ankle as we want, but it’s sometimes fun to look like you’re floating a couple inches off the ground because no one can see what’s keeping your long skirt is so full. It can look really cute to wear a skirt that ends an inch before your petticoat so you can see the colorful ruffles underneath.
What era are you recreating (if any)?
I’ve seen some really short petticoats, which won’t work for any era before the 80s. I recommend a long petticoat for anything before 1910. The 50s fashions usually had knee-length petticoats.