My mother taught me how to do this about 55 years ago, but I have forgotten. I know it is simple but I don't want to make a mistake!
You need a large button and a small button each with four holes. Straighten two paper clips and bend to fit through the holes. Push through the fabric and put the small button on the inside. Bend the wires over and trim to the size of the button. Wind the exposed wires with a thick thread to preserve the spacing. Put a dab of glue on the ends of the wires so they don't scratch or snag anything.