I bought a proper fit ball branded ball which is able to hold up to 300kgs and is anti burst... better to be on the safe side I figured. I couldn't tell the difference between the fit ball and a birthing ball other than the price, so I got the fit ball instead.

I am 165cms tall and it was suggested that I buy the 55cm one. I feel like I should have got a bigger sized one as it is a little uncomfortable to get up off and my knees aren't in the ideal position.
I am using it when in labour and I have been using it for the past few weeks. It is brilliant. I often use it in the shower too for the times when my BH's have been stronger than usual.