Does the pattern specify a specific brand of yarn?
If so, Google it, and hopefully you will be able to find the (average) number of stitches/rows per inch that it will knit up with. With that info, you have something to compare with other yarns. Even different DK brands vary enormously on this count.
If it just said 'worsted', without naming a brand, I would look for a DK that is on the thicker side of the range, though has already been said, it shouldn't really matter for a toy, where the finished size isn't crucial.
I'm another one who likes Wool Warehouse (and you can often find online discount codes for them too).