I think I need a new and better stability ball. I've been using a Reebok one and it came with a hand pump and it's really a pain to inflate. Then only a few days later and it starts losing some air and I have to pump air into it again. Can anyone recommend a good stability ball that isn't too expensive? ($20-$30 range) Which one is Cathe using in her workouts? And how do you all inflate them?