My house is built the exact same way. If I drop a dollar bill in the living room, I have to crawl under the house to go fetch it.

I used unfaced batt insulation held in place with spring wire insulation supports, then covered the entire bottom of the house with Tyvek. SInce that time you can now hire guys to come spray foam the underneath. If I had my choice today, I'd go with spray foam. They don't have to fill the cavities, just a good layer which blocks the air flow.