Double Star is one of my favorite Heinlein novels and has been since I read it for the first time about 50 years ago. It's narrated by The Great Lorenzo, a down-on-his-luck actor who gets asked to play the role of a lifetime, that of "the most important statesman of the 21st century," who's been kidnapped.
Even when I was a kid, I knew this was Prisoner of Zenda in Space, but I didn't care. I loved it. So did a lot of others, as I believe it was a Hugo winner.
Lorenzo begins as a xenophobic, self-absorbed, egotistical actor. But, as another writer warned, "we are what we pretend to be." Over the course of the novel, Lorenzo gets into the role he's playing and becomes considerably more enlightened and humane. At first, he's a fine comic character; by the end, he's a different man.
I think this is as much a coming-of-age novel as Tunnel in the Sky, and a better one. It's not nearly as polemical, and it clips right along in spite of the fact that the only deadly confrontation is within the first ten pages or so and that the villains of the piece never appear on stage afterward. Quite a feat of writing, I'd say.
One problem for some readers might be the lack of strong female characters like the ones in Tunnel in the Sky. In fact, the sole woman is all too much of a cliche, the helpful assistant hopelessly in love with the man she works for.
Oh, and there's carbon paper. A future with carbon paper? I suggest that you don't let this spoil your fun, though.