You will need a cable needle.

You will also need 5(5, 5, 6, 6) buttons. Rowan used shell buttons from Groves and Banks in the UK.

Finished measurements:
Back width at chest: 10.75(11.25, 11.75, 12.25, 12.5)“ 27.5(28.5, 30, 31, 31.5) cm
Finished length: 16.5(18, 20, 22.5,24.5)” 42(46, 51, 57, 62) cm
Sleeve length to armhole: 5(6, 6.25, 7.5, 8.25)“ 13(15, 17, 19, 21) cm

Yarn used:
Rowan Baby Cashsoft Merino
Shade Silver 00106 - 4(4, 5, 5, 6) balls