You're correct sir. Double breasted suits dominated the runways for fall and have been showing up as of late both in stores and on the backs of stylish guys everywhere. And you're in luck, the double-button front is ideal for a lean guy and will actually make your chest and shoulders appear broader. Which is why it can be trickier for men with a fuller frame.
Like any suit today, the key factor is fit. The outsized lapels and shoulders were par for the course back in the day (think old gangster movies or Mad Men's Roger Sterling), but now your shoulders should be snug and your jacket shouldn't extend past the heel of your palm.
Unlike a regular suit, a double breasted jacket hangs in an unflattering manner when unbuttoned. So keep it buttoned—the middle right button only, leaving the bottom one unbuttoned.
Avoid too graphic a pattern. Instead of bright white pin stripes, opt for subtle chalk stripes or traditional dark suiting fabrics in navy and dark grey.
Keep the shoes simple. But since the suit has an air of formality, a pair of monk straps adds a nice touch.
Want to tone down the formality? Ask yourself, "How might an Italian wear this?" Lose the tie and unbutton your shirt's first two buttons, try it with a turtleneck or perhaps with a scarf tucked under the jacket.