I
my BOSU ball. In a big, big way.
Once I was comfortable with the BOSU, and had ideas on how to use it, I incorporated it into my regular routines in place of the step on more simple step moves (i.e. not highly choreographed). For example, Cathe's HIIT 40/20 or XTrain Cardio Leg Blast or Athletic Step. This ups the cardio factor a bit, and greatly increases the balance work and reduces impact (like you, one main reason I wanted to get one). I will also work it into strength DVDs, using it for light weight squats, lunges, hip thrusts, push ups, overheads, side planks, etc.
For specific BOSU workouts, I love Seasun's BOSU Blast workout - both the cardio (basically a step workout on the BOSU) and the core are creative and challenging. If you can find it (some are on youtube), Rob Glick has a couple of good BOSU cardio step workouts. Mindy Mylrea has some great workouts that incorporate the BOSU - not step, but lots of ideas on how to use it. If you get a BOSU, I would definitely recommend seeking out her BOSU Total Body Blast workout. Gives a great workout, and great ideas for incorporating BOSU moves into other workouts.
In short, for me, it was a great purchase. Really helped me achieve better balance goals. I don't know anything about the size - I have a pro trainer I got on a lightning deal on amazon and I am 5' 4" and it seems good to me.
HTH, good luck with your decision!