'... but designers don’t just create one version of a shirt or jacket and then scale it up and down ...'
...could be a bit of a shocker though to see your body-double across the room.
A much more personalised approach is the increasingly popular Bootstrap DIY dress forms. There have been some interesting results on PatternReview with a high satisfaction rating.
could be a bit of a shocker though to see your body-double across the room.