I use Sta-Flo liquid, non-diluted. I pour a couple of gallons in a bucket outside, swish my fabric in it, gently squeeze some of the excess out, and let it drip dry on the clothesline. It dries about as stiff as a playing card from a deck of cards.
People think I'm nuts until they try it. Fabric starched like paper cuts like paper, creases like paper, and sews like a dream. It does not stretch on the bias, and makes for a very precise quilt.