Okay, that makes it easy then. Without any hesitation, I recommend "Vendetta" by Peter David, a sequel to TV's "The Best of Both Worlds" (TNG) and "The Doomsday Machine" (TOS). It had a recent sequel featuring VOY's Admiral Janeway and Seven of Nine, but that was met with mixed reviews: "Before Dishonor". If you want more Kirk & Gary ("Where No Man...", TOS) stories, then look for the trilogy "My Brother's Keeper" by Michael Jan Friedman - it's great! For Khan stories, there's a great duology ("The Eugenics Wars: The Rise and Fall of Khan Noonien Singh") and a sequel, "To Reign in Hell") by Greg Cox. As for "City of the Edge..." (TOS), "Crucible: McCoy", by David R George III, tells what happened to the McCoy who saved Edith Keeler's life and was forever trapped in the past. It's a huge novel, but well worth getting lost within for a week or so. The people I stayed with while reading it thought I was being very unsociable.
The main character is the same as the TOS Klingons but it does mention the bumpy headed ones as well. And a few others too....
The main difference is that Ford speculated that Klingons had extremely short lifespans, which is partly why they cram so much feistiness into their careers. Smooth-foreheaded Klingons (as seen in TOS) are lower class human/Klingon fusions. There are also Vulcan/Klingon fusions and Romulan/Klingon fusions. He also assumes that Spock is a young boy, long before Kirk is born, at the same time as McCoy is a baby in diapers, where most recent books assume that Spock and Kirk are contemporaries.
Well, as the OP was looking for recomendations I didn't want to get into too much detail, just correcting a minor point in Greg Cox's post.
Which turned out to be pretty similar to the explanation we finally got in "Affliction"/'Divergence." And that McCoy is older than Spock. Of course, the bulk of The Final Reflection is meant to be a work of historical fiction written within the Trek universe, so some of its discrepancies could've been presumed, at least at the time it came out, to be dramatic license on the part of the in-universe novelist; lots of historical fiction fudges facts and dates for the sake of the story (just as science fiction fudges physics, biology, astronomy, linguistics, etc.). Although these days the discrepancies are probably far too great to be explained in that way.
As far as Spock's age is concerned, I've come up with a possible in-universe reason to explain to tie in the ageing of Leonard Nimoy with the inconsistency with other Vulcans of Spock's age. This came about as a result of Sarek looking relatively younger than a man of his age (100 something in TOS and over 200 in TNG). Then we had further Vulcans introduced later in the franchise who were of advanced ages by Human standards, but retained the features and physical conditioning of somebody much younger. We had the likes of T'Pol who was in her 60's during ENT, despite her features resembling that of a woman in her late 20's. Whereas Spock's ageing has always been consistent with those of a Human male. So I've reasoned that because Spock is a Human/Vulcan hybrid (and the only one we've seen throughout a considerable period of his life), I think that he ages as a Human would, but retains the lifespan of a Vulcan. Perhaps his ageing would slow down to be more consistent with Vulcans when he reaches a certain period of his life? This would explain the very little differences in Spock's last TOS appearance (as a 50 something) to his appearance in TNG around seventy years later.
Well, keep in mind that the original Spock's aging process ended in the Mutara Nebula in 2285, when he died. Then his body was regenerated and he grew to adulthood at an accelerated pace on the Genesis Planet. I've always figured that the regenerated Spock ended up at an older biological age than the original Spock was at the time of his death.
That's another thing I figured too and I was in the middle of writing it, until it occured to me that it might sound a bit "out there"! The only thing I have against this theory is that his ageing in the later stages of Genesis destroying itself, was more frequent but not as far in jumps as it was during his time spent with David and Saavik. He is found aged around 8-10, before he jumps into his mid teens where he remains until the planet's destruction begins to get worse. From there Spock ages into his late teens, twenties and then begins to age more frequently, without the major leaps in ageing that we had seen earlier. The last time we see Spock before he becomes... (well Spock!) Is when his face starts to show signs of morphing into his familiar facial structure (perhaps an early TOS age Spock?). Once he's aboard the BOP, Spock looks more or less the same as he did in TWOK, perhaps even slightly younger!?