I used an exercise/birth ball with most of my third labor (first homebirth) and LOVED it! It is also great to have around during pregnancy as it helps with posture and core mucles. You also need to make sure they are filled up all the way and taught - or else you will sink in them. You could always buy one try it out and return it if it was too small or too big.
OT answer: I continued to chart with my third for the same reason Katt mentioned - I felt that if my temp stayed up that it was a sticky pregnancy. The problem is that my temp did fall for days and I was extremely anxious thinking sureley I would m/c when in fact everything was perfect. My MW made me promise to stop temping because it was causing me great anxiety.
I also temped with a previous pregnancy and the temps stayed up and I had a m/c, I was pregnant with twins - found out one was a tubal but because my temps stayed up and my numbers went up everything was ok but then I lost that babe as well around 10 weeks.

It is my personal belief from what I have seen that this does not hold true.
Keri