The official reccomendation is 12 months.

We put a Cot Quilt in DD's cot when the nights started to cool off here (after her 1st birthday). We tried putting her in her sleeping bag but she cracked it - it was too restrictive in her mind. The quilt keeps her warm and lets her "roam" in the bed.
We are yet to introduce a pillow but I am thinking about it. Actually, we are going to do it - I just keep forgetting to buy the pillow when I go to the shops!

HTH

MG