am currently reading Star Trek: The Motion Picture (novelization).
"Ex Machina" is the ideal book to follow up TMP with!
"Uhura's Song" by the late Janet Kagan is also a very good "mission" novel of TOS era. Perhaps longer than you prefer but it moves fast.
I prefer novels that deal with technology over relations, but even more than technology I prefer science and exploration... Data rambling on
A great Data whodunnit novel is "Immortal Coil" by Jeffrey Lang, especially if you've already seen "Datalore", "Brothers", "The Offspring" and "Inheritance". There are cameos of numerous AI and androids of TOS, but knowledge of them isn't essential.