That's a cute sweater. That needle size seems like it would make the fabric to dense to me, too. :??
Anyway, there are lots of bulky yarns that aren't expensive. Here's a few - I don't know the gauge on these w/o looking them up, but if they are close they will probably work.
Lion Brand Jiffy
Bernat Softee Chunky
Patons Shetland Chunky solid and tweed
Bernat Alpaca Natural Blends
The above are all at local stores like Michaels, Joann, and Hobby Lobby as well as online.
This is also a good one you can get these online or an LYS.
Plymouth Encore Chunky
There's also some at Knitpicks and Elann that are inexpensive.