Both my girls were posterior. I did all the 'right' things to try and turn them around naturally, but nothing worked. DD2 was born naturally with no drugs, 6 hour labour. I birthed both of my girls on my back (my preference). For me personally, it was easier than being on all 4's. DD2 was 8lb 1oz, so a good size. She was a day early.
Try not to worry too much about bub being posterior. Good luck!