You will need one button - Rowan used #BN1608 from Bedecked in the UK

Finished measurements:
Bust circumference: 39.75(43.25, 47.75, 51.25, 55.5)“ 101(110, 121, 130, 141) cm
Finished length: 18(19, 19.75, 20.5, 21.25)” 46(48, 50, 52, 54) cm
Sleeve to underarm: 19(19, 19.25, 19.25, 19.25)“ 48(48, 49, 49, 49) cm

Yarn used -
Rowan Cotton Cashmere
A. 211 Linen - 6(7, 7, 8, 9) balls
B. 214 Coral Spice - 1 (2, 2, 2, 2) balls