A qualified pick.
5 novellas by Glenn E. Smith supplementing the fan series Star Trek: Phase II/New Voyages. Strange creatures those books. Technically fanfic of fanfic, Smith is very much a hard science fiction writer and the novellas lack the soul that permeates both TOS and its fan productions. Not bad, but №4 drags. Best read in conjunction with viewing the fan series in the suggested order. Ebooks found here https://www.stnv.de/en/novels.php