If you are doing a skull you already have a servo controller. You will save yourself a lot of time and effort if you stick with servos. Servo City has some very small ones in sub-micro catagory. check out http://www.servocity.com/html/hs-55_sub-micro.html
or http://www.servocity.com/html/hs-45h...m_feather.html either one should be able to move the eyes without any problem.