Necklace clasp?

Over break I bought myself two strands of freshwater pearls with holes bored in them for stringing on wire, and I made myself a necklace. I'm quite pleased with it, it's close-fitting and made of gray and white irregular pearls in the pattern of two pearls of one color, then one of the other, then two more of the first, alternated with the same pattern with the colors reversed. I'm not sure what to do about a clasp, however. I just strung them on a bit of wire and made loose knots at either end to keep them on the strand, but I'm not sure what to do about opening and closing it on my neck. I haven't worn it much yet, but so far I've just been tucking the long end of the wire into the knot on the other end and bending it, but it's not terribly elegant, and I'm worried it isn't secure enough. I should probably just try to get a clasp from an art store or something and see if I can attach it. I'd like to be able to start wearing it without worrying it's going to come apart.