This hat is knitted in a thick chunky yarn, which can be duplicated through a few brands. Sirdar’s Sublime Chunky Merino was created for a few exclusive patterns and uses 6.5-7mm needles, to a tension of 14 sts x 19 rows per 10cm. The slightly thicker yarn and using a looser tension than usual chunky yarns gives a gentle, soft fabric to the finished item.
And keep watching as the pattern for matching scarf will be available soon.
A few colours of Sublime Merino Tweed are left in the UK, here is one shop with the yarn
Here's the link to buy the pdf Cloche pattern from Ravelry, let me know if you like it and share some photos in the comments once you've knitted it up.