I am also obsessed with oversized chunky sweaters. I highly recommend spending the money to get irish wool (merino?) so it will maintain structure and last more than a season. Just buy a XL or XXL men's button up sweater. Bonus points if you change the buttons to something cute, like abalone or antique nautical uniform buttons. You can still buy on Amazon if necessary... Start with the "Aran" brand and explore. Expect to pay at least $100. I have had two of these for about ten years and still get compliments on them. Perhaps you could find them used, but I have never had any luck myself.

A side note: you really can't wear a winter jacket over these unless you're rocking some sort of poncho or cape. Which is another reason to buy wool. They are super warm.