MollieSue, I still sit with one foot tucked under me also. I'm an old lady, and have done it all my life. You're right, it is a hard habit to break.
As for the pain in the sciatic nearve pain, lower back and hip pain, the best thing I ever did for that was start walking. I used to have so much pain in those area. After I started walking every day or so the pain mostly went away.