Molly, I've found the best way to get into a good position is to have a little stool (the furnature kind), that I put in front of the loo, and pop my feet on. The aim is to achieve a position where your knees are just slightly higher than the top of your pelvic bone.
This is also a good position for sitting for women who have lower back pain during periods, or for anyone with lower back pain. Next time you get lower back pain, try it, and you will be surprised at how well this works for pain relief :)