This is a really tough area to master properly (not even Hasbro seems to get it right 100% of the time).
I would suggest checking out a fabric store for woven materials. Material with a weave in them are generally what toy manufacturers use when making soft goods for figures.
Take the time to ensure proper selection of fabric SCALE when buying cloth. Bring an action figure with you when you go fabric shopping. Check the cloth weave pattern against the scale of your figure. This makes all the difference between a figure that looks like it's wearing an appropriate garment versus one that looks like it's wearing a burlap sack because the fabric weave is too large for that scale of figure.
My advice is when creating soft goods clothes for action figures, avoid frayed edges on the garments. Take the time to create neatly folded-over edge seams, or pre-treat the fabric edge so that it will not fray when you cut it. Make the investment in a good pair of really sharp cuticle scissors. NOTHING makes sharper, cleaner cuts in fabric than a pair of those! Get into the habit of using an iron to press the fabric garment into its desired shape. It is the slow, patient, deliberate press work with an IRON that will make the fabric work on your figure look like an actual, finished, professionally-made garment... and not just some cloth draped sloppily on your figure.