I use a 1:1 solution of Sta-Flo liquid laundry starch and water for yardage that will be used for backings or for bias cuts. My method, which is easy and fast, is to use a large wall painting brush to apply the starch (I do this on my kitchen island) until the fabric is saturated, toss the fabric in the dryer, then iron with steam. I have tried thicker starch solutions than this and found them more difficult to apply, so I stick to 1:1. The yardage does come out fairly stiff, but this is good -- means the fabric is not going to stretch or distort as I work with it.
Best Press and other sizings do not provide anywhere near the stiffness and stability of starch.
Edit: With the 1:1 solution done the way I describe, long bias lengths do not stretch and do not require a basting stitch, at least in my experience.