star trek novels

I need recs for what Star Trek novels to read. So far all I've read is How Much For Just the Planet and both of the New Voyages. Things to keep in mind: I'm only interested in TOS; I have a short attention span; Kirk/Spock subtext is highly preferred; entertainment value is more important to me than literary quality at the moment.

Also, thank you to everybody who sent the snowflake cookies in my profile! They make me smile everytime I see them. <3333