I used green floral wire, which has been in the craft drawer for years. I only used it because it was there, and I got a long piece and bent it ~14 times. Then hot glued the ends so they would stay together.
If you plan on making Slimy, or something else with wire, I suggest you get residential copper electrical wiring. Sadly, I have yet to try it out, but I will soon! I found out about what wire to use here:[link] Nerdigurumi is quite helpful!