You will need 2 buttons. Rowan used #BF8353 from Groves and Bank in the UK.

Finished waist measurement:
27(31.5, 35, 39, 43)“ 69(79.5, 89, 99.5, 109) cm
Finished length:
14.5(14.5 15.5, 16, 16) 37(39, 39, 41, 41) cm

Yarns used-
A. Cotton Glace Oyster #730 5(5, 6, 6, 7) balls
B. Summerlite DK Mocha # 451 - 1 ball for all sizes