There are several ways. I personally would go down the circle skirt route.
Here's some detail.
What Catnip is wearing
here is a circle skirt with a (organza) petticoat underneath. What I did for it (as I made it ;p) is cut out two large semi-circles out of poly-cotton, then eight semi-circles of organza (had I used tulle like I was suppose to it would have been four, I just prefer how organza falls so I used that instead). Then cut the waist semi-circle in (fold semi-circles in half, place the semi-circles together, and cut a quarter circle). Then you cut a rounded waist band.
You essentially need to do the same thing, but length the skirt so it falls where you need it to. I would also recommend getting a longer petti - in my opinion, using a short petti under a longer skirt causes the skirt to hang oddly.
I used
this pattern piece (don't buy from this site, it's takes ages to come cause it's from the US). However
this one should also be of use to you.
This type would also help you X3