Without doing any math I would think you would need to add 1.5 -2" for every chamber to make sure you have the loft to get to 35*. Assuming that you are going to make seven 6" wide chambers you may need to go as wide as 56" to ensure around 1.5" of loft in the center of each chamber.
Try cutting some strips of paper starting with about 8" long. Put each end of the strip on a ruler at the 0 and 6" marks and see what the curve gets you. When you find a length you feel will work, multiply by 7 and that will be the width you need plus hem allowance
This pic from Dutch's gallery shows a good example of how to mock up the quilt before starting to sew. Went way back to 2008 to find this one