American patterns terminology

Worsted is dk, it will work fine

If it’s a toy I’m sure it won’t matter whether DK or Aran. I’d stick with DK.

If you look on Ravelry it defines all the different yarn thicknesses by the number of 'wraps' they make around a knitting needle. So you could carefully wrap your yarn around a needle, count the number of wraps to an inch and then check it against their yarns.

Another way to compare the thickness of a yarn is to see how long a skein/ball is for the weight of it (its usually on the label/band. I've been experimenting with Scandinavian yarns to make Icelandic style sweaters and have had to convert. Thus if its a 100gm ball and is 100mtres long its Chunky......if its 100gms and say 120mteres its nearer to Aran.....whilst 100gms but 200 metres its double knitting etc.
I've found a lovely Wool website called Wool Warehouse that stocks a huge range and it gives lots of information for each of its very wide selection of yarns. So when you realise that you get a huge length of yarn for a given weight you know its going to be a finer yarn.

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).

Thanks for all your suggestions- much appreciated. I shall post a pic of weasel when he’s finished - in the meantime I’ve shared my bobble sheep!

He is FAB!

HildaW. I love Wool Warehouse too!