Have seen and heard many people say it is good for baby and bump to bounce on a ball.
When should I start doing that? I'm 24+1. Is it supposed to encourage baby to go head down? If the baby is going to move head down when does it usually do it? It wasn't head down at my 20 week scan and I have no idea how to tell if it is now 
And also, is any ball ok? I have a yoga/gym ball but was at labour ward for an anti-d on Friday and their birthing balls were much larger than mine. Don't want to go to the effort of pumping mine up if it is going to be crap 
Sorry for sounding pretty thick
This is my second pregnancy, you'd think I'd know something about this by now, but I feel I know less than ever!