I would be tempted to find another pattern for a similar beret. Are you on Ravelry? There's a free pattern that looks very similar, but calls for size 11s with aran weight (and an excuse to use Malabrigo) yarn
http://www.ravelry.com/patterns/libr...slouchy-beret# .
You could also search and see if anyone has used your yarn for a beret, and what pattern/needles they used.