I just read TOS: From History's Shadow by Dayton Ward a couple months ago, and I loved it. It does combine elements of DS9 and Enterprise with a TOS story, so as long as that doesn't knock it outside of what you're looking for, I would highly recommend it.
TOS: Strangers from the Sky by Margaret Wander Bonnano is also worth a read. Just as a warning, this one came back in 1987 and does contradict the movie First Contact.
TOS: Troublesome Minds by Dave Galanter is also good.
TOS: Strangers from the Sky by Margaret Wander Bonnano is also worth a read. Just as a warning, this one came back in 1987 and does contradict the movie First Contact.
TOS: Troublesome Minds by Dave Galanter is also good.