Bunhead bun pins, XL, choose color to match hair, by Capezio, from Capezio online or Amazon. There is a trick to putting in bun pins for max hold. Do not put them straight into bun at base. Stand on end in a 90 degree angle to base of bun, inserted inside some outer strands of hair. Push in toward scalp (no need to puncture scalp!), “turn the corner” and slide slightly upward and into bun.
And, there are endless YouTube videos. Search “military women’s bun” and “military sock bun.”
Posted by someone who can still put hair in a regulation bun in about 20 seconds, from comb to twist to buns to pins.