The published adventures are limited, true. But I can understand if you feel nervous tweaking your own stuff up - when you're first starting out, you can definitely be worried about "doing it wrong" and "ruining it for everyone". However, you're on the right track already by listening to your players. Take Thunderspire, find what you like in there (and what you think they'll like), and twist it for your own purposes. If you're getting nervous going off the beaten path at first, Thunderspire is a great place to get your feet wet - take some of the NPCs and side-plot hooks that they mention and expand them out a little - if you're looking at building your first encounter from scratch out of the monster manual, stick it in as a random encounter in the labyrinth. The more you do on your own, the better you'll get at it and the more comfortable you'll be with it. And it really doesn't take a ton of time - I brainstorm up ideas for the games I DM during the week, then actually sit down and pick out my monsters and stat things up in the half hour before the players show up.
In summation, because I started to ramble a bit - the published modules do not live up to the DMG's advice - you need to inject your own personality and flavor into the game to be truly great, and no one knows your group better than you do. That being said, you don't have to jump straight into the deep end - use the published stuff as a framework and build off of it, or if you're free-styling, rip chunks out of the published stuff and slide it in. And steal ideas from everywhere - no one's going to be offended that you're stealing a piece of your plot from Star Wars or Naruto, because they're the main characters, so it won't turn out the same way that it did in whatever you're stealing from.