If changing fabrics is not an option - it wouldn't be for me after I've already started - then just starch the daylights out of it. Regardless if you've pre-washed your fabrics or not. I use liquid Sta-flo starch mixed at a 1:1 ratio - half starch; half water - and use a generic spray bottle from either the dollar store or a discount store.
I also suggest, when starching, press your fabric with an iron. While still warm, spray with the starch. Wait a minute or 3 to let the starch soak into the fabric and then press again with your hot iron. If the fabric is really thin and wrinkly, you may want to use a higher starch ratio such as 3/4 starch to 1/4 water. Lots of options when using a liquid starch. There are also other brands and may be available in the laundry aisle of your grocery store.