I am a newb as well, but I picked up a sparco ribvest based on advice from a member here and when I get in my seat it is tight enough that I can not move at all. It is snug enough that I think maybe it is too snug. But when I am driving all I can think about is how any bigger and I would get tossed all over the place.
So from my limited experience, dont skimp on the ribvest and get a nice tight fit on the seat.