I have done this hat in four sizes but it is easy to customise the fit by increasing (or decreasing) the number of ridges you knit. I think this design is perfect for self striping yarn and I have been using King Cole Riot DK. I had plenty of yarn left from 100g to knit a flower and a disc, you could do two flowers if your prefer. I have given a suggestion for a flower pattern but there are plenty of alternative patterns available on Ravelry.

The adult sized hat including any flowers takes 50g DK, I knitted a toddler hat and cowl with 50g