I like thongs and was lucky enough to come across THIS pattern for this one. It calls for crochet cotton and a B hook. Being a little on the larger size, I used a C hook and sock weight yarn. I started one in Panda Cotton, but didnt have enough yarn to finish, so I found a skein of Sockina Cotton in my stash and tried using that. This is how it came out.
I made a couple changes in mine. I made it in one piece and connected the sides instead of using ties and I left out the side straps in the back. But it fits....and comfortably! I am going to finish the other one as soon as I get some more yarn.
If you dont like thongs, you could make the back the same as the front, only a little larger....the pattern is repetitive. There is also a chart that makes the pattern very easy to follow, however it is hand drawn and very small, so you might need a magnifying glass or a way to enlarge it, but it DOES help. The link page is in mostly in German but at the bottom there is a PDF link for the pattern in English. I hope you give it a try.