First, what are sleepy eyes? Sleepy eyes is when the doll has 2 pull cords: one for opening the eyes and one for closing and changing the eyes. **I did recently read that if you leave your doll asleep too long it can warp the eye mech.** Nothing extra has to be purchased or anything.
This is the method that requires your doll's head to be open. There are other tutorials out there that does not require opening.
Pay attention where the pull cord is located once you open your doll's head. That is where one of the cord will need to go again. The second one goes in place of the spring. I, personally, remove the spring.
Once the new cords are attached on the inside, one cord comes out of the original hole and one comes out where the spring used to hang.
I think some people have both chords come out the original hole. This is your preference.
I use 1/8th inch ribbon as my pull cords. I have never had one break. A tip to get it through the eye mech hole- Cut the ribbon at a sharp angle and then melt it, at an angle, with a cigarette lighter. Then used a pin to poke it on through the hole. Doing this also helps when thread beads onto the ribbon.
Also, be sure to use long ribbon and trim it later!
** I assume no responsibility in the outcome of this tutorial. If you use this as a guide, you do it at your own risk, or your dolls risk.**