The dressmaker's serenity prayer/meditation:
Please grant me the serenity to refuse the garments I cannot sew/alter; courage to sew/alter the garments I can; and wisdom to know the difference...
By far, the greatest challenge I have had in dressmaking, is sewing for people with scoliosis. When the challenges are skeletal, postural, and anatomical, it makes any dressmaker seem completely inept. I have discovered that many who have been in the profession for many years, simply say "no" when asked to do this work.
The challenge, as I see it, is that the grainline on a curved body (depending on how it curves) will not simply hang straight where you put it. If you over-fit a garment, it becomes impossible to honor the grainline, and if you try to create any design line that is meant to look "straight", the question becomes "Relative to what?" Are we making a straight line down the center of the wearer's body, or is the line meant to be straight as it relates to the horizon? Do we "cheat", and create something between the two?
In the meantime, the process can frustrate a person to no end.
So, the solution, as I see it, for the person who is well-financed and maintains a stable enough weight to do so, is to get a custom made dress form, so endless fittings aren't needed. But, guess what... when you ask the custom form makers if they will do it, and explain the challenges, some of the very best companies will still tell you "no".
As I see it, the only true fitting solution, if you want to create complex designs, is to have a body cast made, using that to create a dress form. Well, that, or keep it simple, and relax your fitting standards a bit... (my recommendation).