The book my MW gave me also says to keep your knees lower then your hips. It also suggests sitting forward over a beanbag when watching TV etc, sitting upright with the soles of your feet together knees out to the side, avoid squatting as it opens your pelvis and encourages baby to move down (wait until bub is in good position before doing this) and not crossing your legs as it reduces the space in the front of your pelvis and opens it up at the back.

I hope some of that helps.