If it's draft that is getting you, and you can fit down there, the easiest fix is to go around with caulk gun / canned spray foam and just fill up any holes/gaps on the outside wall. Once you have the draft fixed then you can decide if you need insulation (Which you likely do, but air sealing will make a BIG difference) Make sure you have a vapor barrier on the floor, and it is completely sealed. If you decide to insulate, you can put up fiber glass batts on the outside wall. This is assuming the crawl space is dry. This is the BANG FOR BUCK option, I did this with R38, and my crawl space has been 10-20* warmer since. If your gonna fork out money, I would simply follow everyone elses advice, and pay a professional to come spray foam the perimeter wall. Air tight, water proof, with a high insulation value. Nothing wrong with that. I'm not a fan of just insulating between joists, bu to each his own.