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The PPFA book on Textiles and Needlework recommends the following:
-Batting, 100% punched polyester, for loft or padding
-Fabrics, such as unbleached muslin for additional support or attachments
-Polyester film, for support under dimensional features such as waves, ruffles, etc.
-Acid-Free Tissue Paper, unbuffered, as filler or support.
I'd recommend getting the book to learn the full details of which material is most appropriate and how to properly apply them.
Sounds like a fun project. Share pictures when you are done!