Lace Leaf Hat
Although Lush is classified as an Aran weight yarn, the fuzzy, airy quality allows it to be knit at a much tighter gauge and still produces a supple fabric. If you substitute, I would suggest a DK or light worsted to obtain gauge.
Could also be knitted in a DK cotton yarn like Rowan Handknit Cotton for a cooler version. Remember if you change the yarn weight, you will likely get a different row gauge, even if you are able to match the stitch gauge.
NOTE: If you want a tighter fitting brim, drop another needle size (US 3) in the garter stitch brim or try a k2p2 brim instead.