I worked with all three, like all of them, eventually used Spring Data's because application was itself based on Spring Boot and that made data access play very nice with the rest of the app. But both Morphia and MongoJack could be used effectively too. I suggest to play for a couple of days with each and decide. There most certainly are other libraries, but these three I had experience with.

Also, I do not feel it's coupled, more like—well integrated. Many of its subsystems can be easily replaced by 3rdparty, e.g. in one project I work on we have jax-rs/jersey instead of Spring MVC.