Heyweknit has made this baby cardigan, and it is knitted in one piece with minimal to sew afterwards.

Before getting started you will need to make 2 small balls of yarn on 6 g each, for making the sleeve edges. All the edges are knitted at the same time as the the basic cardigan.

The pattern has a good description, on when you need to remember the change of yarn color and the stitch variation.