I could go into all the philosophies inspired about sex in religion.
I don't think that is what you're asking due to the term "vanilla".

From what I understand about that religion is that husband and wife are expected to mate using what is commonly called "The Missionary Style"
Facing each other lying prone with the woman beneath the man.

"Doggie Style" is not permissible because it alludes to animalistic attitudes.
Likewise, any position/style that does not sanctify the act is considered sin.

What is also implied is that a man should never spill his seed unless in the act of procreation.
Therefore, just having sex because it feels good is also a sin.

It is also implied that the bed is the holy place of procreation so sex in the kitchen, porch or living room is also considered a sin.

From what I conclude from my understanding of the religion in which I followed, there is no such thing as holy sex. Any sex for pleasure is a sin. Even with husband and wife.

Copulation is for one purpose only, to sire a child.
Be fruitful and multiply and all that jazz.