Eh, supplements (smiley: eyes) traditional prep is the way to go.
You should go to kavasseur's blog and see his ratings on different kavas, he'll let you know which ones are sedating an which ones are stimulating. His blog is a great reference.
From my own personal experience, I'd say to go with a nice mellow Hawaiian kava, maybe give Paradise Kava's Hawaiian awa a try, I find that stuff is great for sleep and tastes great. I would recommend Rava by Rex Fiji Waka or Tudei, both wonderfully sedating, but if you've only ever taken supplements, you might find them a little harsh. Vanuatu3 from Kava by Rex is also great for relaxing and falling into sleep.
I hear Bula Kava House has a Boroguru (not to be confused with their borogu) which is good for sleep, but I've never tried it.