Rich, I'm a similar height and had the same problems when I was younger.
Difficult to say without watching you but I would guess you are coming up too early, when you are that bit taller it is very difficult to readjust and get back down.
The key is to stay in your crouch until the ball pitches, I sometimes actually take the ball still in my crouch. If this doesnt feel comfortable then work on only coming up with your knees, not your head, your back or most importantly your gloves. Practice going into your crouch and then try and straighten your legs to a standing position without moving the rest of your body, this will keep your gloves low, your head still and give you a good position to adjust if necessary.
Hope this works for you