Hi Anna…
Normally Seamly2D is used as a made to fit application, but if you make a pattern to fit a standard sized dress form, you can easily grade to another size by creating standard size measurements. Basically you would just be reproducing the size table on any given commercial pattern with a set of vit measurements.
Maybe take a look at this topic I made on a dress pattern I took off a draped pattern made on a standard Wolf dress form… Shift Dress Pattern