Book recommendations are kind of out of scope.
A Sit & Go is a mini tournament. Because of the payout structure a chip you lose is worth more than a chip you win. You need to stay alive. You should be more selective about your hands.
Players like Negreanu will play a range of hands and go for pot control. He has some books out.
Old school Harrington on Hold'em, Volume II: The Endgame covers tournament strategy and math nicely.