DIY Duct Tape Mannequin - Modge Podge fabric on instead of hot glueing it. Also make full form with arms and legs?
Use expanding foam from the hardware store to stuff the dress-form.That stuff hardens well enough you will never have to re-stuff it, but still ok with pins, etc. To lessen volume, first stuff with packing peanuts or crumpled newspaper. Be careful to keep the body doubles' shape the same while the foam expands. Working with small sections at a time should help.