You will need 5(5, 5, 6, 6, 6) buttons. Sirdar used their button #B5611-0902.

Finished measurements:
Chest circumference: 18.5(20, 21.25, 22, 22.75, 23.75)“ 47(51, 54, 56, 58, 60) cm
Finished length: 9.75(10.75, 11.75, 12.5, 13.5, 14)” 25(27, 30, 32, 34, 36) cm
Sleeve length: 6.25(6.5, 7, 8, 8.75, 9.75)“ 16(17, 18, 20, 22, 25) cm

Yarn used:
Sirdar Snuggly Cashmere Merino Silk DK
A. 301 Mother Goose - 2(3, 3, 3, 4, 4) balls
B. 310 Red Riding Hood - 1 ball for all sizes