Hi Mousie,
There is a wonderful shop here in the truckee meadows that sells all types of aroma therapy items. It is called Lavendar Ridge. They sell the bags filled with flax seed instead of the normal rice. The rice can burn and smell terrible.
I made sets of these and mailed them to my in laws a couple years ago. I bought the flax seed at a store that sold it in bulk, and the lavendar oil from the lavendar ridge store. (pricey but, wonderful) What I did was to draft a pattern for the eye pads and a larger one for the neck and other areas of the body. I used a very nice micro fleece in a floral print for the front and matching solid for the back. I then made a muslin bag to insert into that held the flax sewn into it. The scent is created by the drops of the oil. (Very little is needed) and then I included a small vial of it to refresh the scent when they needed to.
They were a big hit. They only take thirty seconds in the microwave and stay warm for about an hour. My sister in law used it on her knee and it fixed her knee problem enough that she didn't have to have surgery on it. Crazy ... huh? I bought a small colorful matching plastic basket to hold the sets and the other little bath salts and things that made up the "spa" sets.
I think I might still have my old pattern I made, I am not sure. But they were kind of a bone shape with rayon cord circle attached at the sides. I added a nice plastic bead to adjust it to your head and hold it on from the back of your head for the eye pillow. And the other was just a rounded off rectangle. I did use a corded seam on everything, More for the looks than anything.
Anyway try and find the flax seed. It works much better and stays warm longer and doesn't stink.