Peckish, Some of the members of my quilting group have been making their own spray using potato based vodka for a long time. Some like it, others not so much. Isn't that just the way things go.
If it isn't really starch, why not just spray with water. I find that many fabrics have enough "stuff" in them that all they need is a little freshening up with a spray of water. I can just see them shrinking and going ahhhhh.
So, back to the original question. I use starch and not sizing. It works for me. Perhaps it is what do you want to accomplish. Simply iron out wrinkles? Water works just fine. I starch the stuff'ins out of the fabric when cutting on the bias and then my accuracy improves.