I consider myself an experienced knitter, but that would be a challenge I would really hesitate to take on. It would be simple enough to add width to a pattern by determining how many stitches per inch you will knit with the yarn and needles you choose and adding stitches. However, there are several other things to consider. When you add width, you may need to adjust the neckline as well. And the shaping (if any) will need to be adjusted too. As much as you may love this pattern, I think I'd choose another. Sorry. I don't mean to be a downer.

I searched and found the pattern you are speaking of. It's a simple shell and matching cardigan. Something very similar should be easy to find and you might check Ravelry for it.

Has anybody knitted a baby surprise jacket by elizabeth zimmermann