This is the basic pattern I use for a plain single stitched crochet frik kippah, made with fingering weight Merino wools, usually held double.
I stitch tightly, so you may need to experiment with a size hook that is larger or smaller than my usual 3.5mm (6/0) hook to get the gauge I do.
As you work with different brands of yarns (and their interpretation of yarn weights), you will come to know what size hook works best with what yarn.

For a plain wool kippah, I suggest Brown Sheep Company wools. They have a good color selection and the yarn is easy to work with, even worked with a single strand.