If a skirt is eight inches below the knee, it does not reach the ankles, unless the girl is extremely short. But it would be better to wear a skirt that does reach the ankles.
If sheer stockings are immodest, then bare legs would also be immodest. I do not see why tights would not be allowed as an undergarment.
It is a wonderful sight to see a woman dressed modestly. I bet a woman woman who really wanted to please God would dress as modestly as possible. If Muslims can dress modestly without any supernatural virtue, I do not see why it is so hard for Christians to do so as well. When I see how the Muslim women dress, I think it is good; that is how the Blessed Mother dressed during her life and that is how she is dressed when she appears in apparitions.
Shouldn't we strive for the ideal instead of for the minimum? We are told to be perfect and that only those who are perfect can enter into the kingdom of Heaven.