As I knit this for my daughter the pattern is only available in size M.

I’m knitting very loosely. It is possible, that you need to use another needle size to obtain the gauge.

The yarn, that I suggested unfortunately is discontinued. I discovered a bag with the yarn in the deepest corner of my wool wardrobe and thought: “Oh great, that is the right yarn for a vest” I’m sure you will find another wonderful bulky weight yarn for your vest project. :-)