Someone's already suggested leveraged ETFs. If you need more leverage on top of this then you could always leverage your account 2:1. On a product such as SPXL that would give 6:1 leverage versus SPY. What's an ES contract, about 20:1? Plus you'll be able to control your position size much more...
I haven't experienced any slippage but only started trading recently. Is there no way to avoid this, like avoiding high volatility market conditions? Can't you look at the depth of the bid and ask on the DOM to get an idea of how much liquidity is there before you place a market order?