Upvote:1
Depending on your experience level. For beginners, best to focus on generally keeping body straight, but staying relaxed and keeping it sustainable for long sits. People tend to have problems and deformities, don't force it into what you imagine a correct perfect straight posture is. Just have the intention to be straight, relaxed comfortable, let the body slowly correct itself over the years (doing yoga, other kinds of therapy to address problems with posture outside the meditation sit).
For intermediate, this article dealing with spinal alignment specifics will help: https://notesonthedhamma.blogspot.com/2019/07/04-ujum-kayam-panidhaya-maintaining.html
For advanced, there's what I call the Jazzy effect: https://lucid24.org/tped/j/jasi/index.html