While working your way up on the Lat Pulldown Bar (if that's the route you choose to go) you might want to try "combo" pulldowns. These mimic the sternum pull-up to some degree. And you can do them palms-facing or palms-away. Wide or Close-Grip.. Begin the pulldown until the bar is about level with your forehead, back absolutely vertical. As you go past your forehead on the way down, lean back to quite a degree and bring the bar right down. One fluid motion, not two. As the bar goes back up, reverse the situation...in one fluid controlled movement. I'm a fan of Mastover's advice too...start weighting your pullups/chins at the earliest opportunity if you can. Doesn't have to be a huge amount to start with. Hell...2lbs will do it.