What are the ways used by Sith to dramatically extend their lifetimes?

Question

One of the point brought up in the debate about Dark Side vs Light Side power is Dark Side users being able to use the Force to dramatically extend their lifetimes.

One of the ways, EU says, Sith achieve that is through Transfer Essence aka forcefully-possessing-another-body, a dangerous ritual with high failure rates in possession and 0% failure rate when it came to the destruction of the user's original body.

What are the other options available to the up-and-coming Sith Lord wanting to live longer / stay younger etc and with what costs?

Answer 1

In the books Dark Apprentice and I, Jedi, we find that ancient Sith Exar Kun had managed to survive as a spirit inside a temple on Yavin 4. In other books, we learn that he had drained the life force of almost an entire species using his Sith alchemy, to become a spirit without a body. This act destroyed his body and most of the surface of Yavin 4.

Method: Sith alchemy to drain life force of other beings to transcend mortal flesh

Drawbacks: Kill targets, destroys own body, does significant damage to surroundings, spirit form can be contained by a Jedi wall of light

Note: EU only, so not Disney canon.

Answer 2

In what is now Legends-canon, Darth Plagueis' skill with the Force developed to the point where he would eventually have been able to halt the aging process:

The scars that had grown over his wounds had abruptly begun to soften and fade, and he had begun to breathe more freely than he had in twenty years. He began to sense that not only were his damaged tissues healing, but his entire body was rejuvenating itself. Beneath the transpirator, areas of his skin were smooth and youthful, and he knew that eventually he would cease to age altogether. (Darth Plagueis, p348)