Definitely the body protector is a good idea. Try to get one that is Beta Level 3 certified (the Intec brand ones are priced very well--it will have a purple tag on it somewhere) and that fits you right (i.e. the bottom flap goes all the way down to your pelvis and it completely covers your rib cage). Also ALWAYS wear a helmet, this is something I feel that they often don't stress enough in Gymkhana...you NEED an ASTM/SEI certified helmet (look for the SEI tag on the inside of the lining) that fits your head well (so you can bob your head without the helmet moving at all, but not so tight it gives you a headache). It's always better safe than sorry, even if you feel that you are experienced and you have a "safe" horse--horses are horses, and even a pony weighs way more than you do. And even arena sand is a pretty hard knock when you bang down on it from a horse's back... :P
What Pony Club level are you? If you have a safe horse that can take you up a level or two, don't go rush to buy a new one quite yet. There is nothing wrong with an old, dependable horse, especially at your level and when you have maybe had some bad experiences, as long as he/she is sound. The "golden oldies" will set the tone for your learning and your riding career later. There is nothing worse than being "overmounted," meaning your horse is too strong for you...don't go buy a flashy jumper and end up with a horse that you are scared to ride! That said, if your old horse is getting too creaky to jump well, then you might want to consider looking for a new one. Just keep in mind that the most important thing is that you feel completely safe on its back and that you have a good instructor to help you evaluate all the horses you will end up going to test ride.
^^Did I understand your first question right? I was reading it again, and I thought at first you were asking about getting a new horse, but I got a little confused at "My old one is Childs Small and is FAr toooo small, I tried it on today"...sounds like you were talking about tack or something. Was that just a typo or did I totally just rant about the wrong thing?
He knows when you're happy; He knows when you're comfortable; He knows when you're confident; And he always knows when you have carrots.