Dear 100 Hour Board,
Anatomy has always kind of weirded me out, but I'm about to get married and would like to go into my marriage not completely clueless. Are there good LDS "How to have good and healthy sex" books out there?
Anatomy and sex are different things, so if it's just an anatomy lesson you're after, these books might not help you as much. However, one book that someone gave me when I got married was Becoming One: Intimacy in Marriage, by Stahman, Young, and Grover. The authors are all LDS doctors, and two of them are men and one of them is a woman, so they give pretty comprehensive advice.
This website also has a list of books that are apparently great for learning about sex from a Christian standpoint, although I can't speak personally for any of the books on the list. Amazon has good reviews for them, though, and I've heard about some of them before in good terms, so you might like at least a few of them.
Also, from your question it looks like you're a bit reticent about talking about sex. I know it can be awkward, but this is just my plug to please, please talk with your fiance about sex. It's entirely possible that neither of you will really know what you're talking about yet, and your ideas may well change after you're actually married, but it's important for both of you to know what your expectations and boundaries are. And if you think it's awkward to talk about sex with your fiance, just remember that you're actually going to be having sex with them soon, and communication is key.
It's definitely a good idea to have some kind of background knowledge in human anatomy and sexuality, but I don't think a clinical understanding is necessarily going to assuage all of your concerns or nervousness. I could be way off base on this, but if both you and your future spouse are LDS, there's a good chance that he/she is just as ignorant about sex as you are. I definitely second Alta's advice to talk about sex with each other, but it might also be helpful to keep in mind that sex is a learning experience. It may not be great at the beginning, but the more sex you have, the more you'll grow to appreciate and understand what you like and what your spouse likes. You'll learn and grow together, which will make for a good and healthy sex life.
As a disclaimer, I'm just about as single as you can be, so I can't claim to be an expert on the subject, but I would imagine having sex is just like any other skill: it takes time and practice to improve and excel. Starting out feeling clueless or ignorant doesn't mean you're doomed to mediocrity, and you and your spouse can work together to fulfill each other's needs.