You will need 3 buttons for the shoulder closure. Patons UK used #Bn1150 from Bedecked in the UK.

Finished measurements:
Back width:
26(27, 27.5, 29.5, 30.5) cm 10(10.5, 11, 11.5, 12)“
Finished length:
23(25, 27, 29, 31) cm 9(9.5, 10.5, 11.5, 12)”
Sleeve to underarm: 14(15, 16.5, 20, 21) cm 5.5(6, 6.58, 8, 8.5)“

Yarn used:
Patons Fairytale Merino Mix Dk
A. 01001 White - 2(3, 3, 3, 3) balls
B. 01053 Sky Blue - 1 ball for all sizes