Its along the lines of a hanfu, not a kimono, I believe. Though korean clothing terms still illude me mostly, so im suggesting a chinese style.
How you do this is pretty simple. Instead of cutting all panels straight, you need to angle them out from the waist down like so / \
The wider the bottom of the triangle, the wider the bottom of your dress will be in the end.
You could also do it in a kinda Hanbok style, where the top and skirt are separate and the seam hidden by the waist sash.
Here isskirt patterns if you go the two piece route: