I use Stay Flo starch concentrate. I can mix different "custom " strenghts depending on my needs. I can only find it at Walmart. It 's in a blue plastic jug . The key to starch is to let it soak into the fibers, before ironing. Often I let it hang dry over night if I am using a strong mixture.
In a pinch I will use an airasol then its usually Niagra with a hint of lavender , very nice delicate smell.