The cheapest place to increase your aggression postflop is on the flop. Start raising your TPTK hands and raising flush and oesds for free river cards. You'd be surprised at how many c-bets you pick off on the flop, and how often you get checked to, to either fire a second barrel and take it down or to take your free card. Raise weak-tight opponents when they make weaksauce bets and you have a piece. Raise with air in position when checked to. Raise raise raise...