What ball size and post height are used?

Bee Netball uses a size 4 ball (one size smaller than the adult size 5), suitably inflated, plus lowered posts:

England Netball's Domestic Rules Guidance says that adjustable posts should be shortened to the right height. If a post is a fixed length, the ring is lowered instead. For Fliers, a floor spot or other target can stand in for a goal if needed.