Just as I learned that learning the bow hold quickly and effectively can be accomplished with an accessory, I have also come to view the violin hold -- which is what I am thinking you are meaning by "posture" -- as largely an equipment issue.
Here is an excellent site to learn about the importance and function and options of chin rests:
http://www.chinrests.com
and here is my favorite shoulder rest for the majority of my students:
http://www.cicaviolin.com/shres0for473.html
Best Wishes,
Ruth Brons
Inventor of Things 4 Stringsinstant bow hold accessories
www.things4strings.com
You will find Results regarding the patented Things 4 Strings® bow hold accessories for beginning violin, viola and cello students from hundreds of private studio and classroom teachers, method book authors/editors, national and international string pedagogy leaders, young and adult students, and parents here.