Slits being a problem has no basis in halacha. The requirement is that the knees and above be covered at all times. Most people feel that you need an extra few inches so that the knees are covered when sitting, as well. So any slit that ends 3 inches below the knees is totally fine, as the entire skirt could end there. Anyting you do below the 3 inch line is OK. You can have a slit, you can have elaborate cutouts, you can eliminate everything, you can cover down to your toes, you can embroider a picture of your dog, whatever you do is fine, as long as everything is covered above the 3 inch point.
We have enough halachas, why invent new ones?