If you are preparing embroidery samples that are to go on a specific fabric, then you should always do your samples on a fabric that is as similar to that of the final object as possible. That will show you, and your customers, what it will look like on the finished product.
Sometimes, if the fabric you are testing on is too different, you find that it stitches up completely differently and looks completely different - and that difference is not always good.
Have a look in the dressmaking fabric area rather than the craft area for the sample fabric. You will probably find the right stuff there, and a lot cheaper than craft fabrics.