If you have several pillows to make, it will be worth making your own forms.
My favorite filler is the Soft Touch brand. Their brand never gets hard or lumpy. You can purchase the Soft Touch loose filling, or you can buy their pillow forms (easier, but more expensive). If you need to make several pillow forms, buy the filler in a large box at the craft store. It’s a better deal.
Window treatment lining is a perfect fabric for making pillow forms, if you have scraps after a curtain project. Any inexpensive poly/cotton works well.
Simply cut two squares that are 1″ larger than the desired size for your form. Either surge all the way around, leaving 4-5″ open on one side, or sew and zig-zag the edges and leave the same type of opening. Stuff with fiber until full but not tight.
Remember, we want a little movement. Push the fiber into the corners, working it around to smooth it.
Push the filler back away from the opening, pin the edges together, and sew it closed with a sewing machine. Fluff it out again at that edge. Or, just whip-stitch the opening together by hand. Easy-peazy!