I found this lovely Japanese pattern at this address:

ダイヤ透かしのベビー胴着(70cm)・レッグウォーマー
https://www.amuuse.jp/recipe/detail/amu-567.html

with direct free PDF at:
https://www.amuuse.jp/recipe/AMU-567.pdf

The instructions are very explicit, although I don’t know any Japanese…
Bottom photo is from the website. Above is my interpretation of the pattern.
Very happy with the outcome.

Cast on 121 sts, made 7 rows of bottom band, 2 rows of St sts, then started the pattern (which is 10 sts repeat by 12 rows). Made 4 x 12 rows pattern reps then started arm decreases. V-neck decs started on 10th row of last pattern repeat and made basically every other row…well followed the chart given by the pattern…up to 10 sts left for shoulder, for fronts, and 29 sts for back.

For armbands, I worked flat, I picked up 59 sts then decreased to 58, 57 and last 56 sts to a total of 5 rows and then on 6th b/off using Russian bind off technique. So: 1st pick up the sts, row 1 k, row 2 k, row 3 k, row 4 p, row 5 p, row 6 Russian b/off.

For front band picked up 5 + 67 + 29 + 67 + 5 = 173 sts and made it in the same manner as for the armbands … phew…

Made an I-cord of 2 sts only, long of cca 26-27cm un-stretched and sewed where I first started the V-neck decs.

I used less than 85 g (cca 82) white 8ply acrylic and after blocking, it measures: length cca 34-35 cm; width at armpit cca 31 cm x 2 => 62 cm (chest).