I have used garter stitch in this sweater for three reasons.  1) Garter stitch is simple and soothing to work since you knit every row.

2) Garter stitch lies perfectly flat so you donʼt
have to fuss with a curling edge on your sweater.

3) Garter stitch makes a ridge or horizontal line of bumps every other row on both sides.  So you can use the ridges to
keep count of where you are in the pattern.

I recommend sock yarn for baby sweaters because it is

1) washable,

2) has wool content for warmth and

3) comes in better colors than typical baby yarn.  I recommend a hand dyed yarn for this sweater since the garter stitch is most beautiful when the yarn has some subtle color changes.

The pattern is available on Ravelry

I have some hand dyed sock yarns available on my Etsy site