If you would like to insert eyes in your doll head as you are sculpting the head you will need a pair of glass eyes, beads or polymer clay eyes. These can be made or purchased.
Here is one technique for making eyes for your doll from polymer clay and painting them:
Another technique is to roll tiny balls of polymer clay and soft fire them (Tip: place eyeballs in a glass and use your heat gum to "bake" them). Then insert the soft fired eyes in your doll head as you sculp the head. The eyes are painted after the doll head is baked.
You could also purchase ready made eyes; available in glass or polymer clay(don't use the acrylic pre-made eyes as they don't take the heat when you bake your doll) and some purchase white jade beads.
So what size is correct for your doll? Click this link and scroll down to Human; the chart has the size in millimeters for various scales: http://www.noadi.net/EyeSizes.html