When I measure for my waistline I add 2 inches for ease. This is not binding to me, but it is... not snug, but ummmmm, comfortable. Two inches ease for my hips, a skirt comfortably skims them. My opinion is not from experience with drafting the bustline, but I think around the bustline, I would want a total of 4 inches of ease. this would allow for deep breaths, and flexing of shoulders, pulling of the garment as you work without tearing, etc.