Simple crocheted buttons, pattern includes convert to knit.

From pattern:
“MATERIALS: Use the same yarn or a contrasting yarn as in the garment. If the garment is crocheted, use the same hook size. If the garment is knitted, use a hook the same size as the needles used. For example, if the garment used 4.5 mm needles, use a 4.5 mm hook. A smaller hook will make smaller buttons. A larger hook will make larger buttons.”