Hi Amy, as of now, e-collar technology is about as miniaturized as they are going to get to keep the 100 stim levels, tone, vibration etc. In fact, the ET-300 Mini is the smallest e-collar on the market but everything keeps getting smaller and smaller. We are working on a new model called the Nano which will be the smallest on the planet so keep an eye out for it.
For that size dog you may want to just try our vibration only e-collar; PG-300 and ask use to swap out the Biothane strap with the lighter Nylon strap. This model has 100 levels of vibration and will vibrate that little guy like that across the kitchen floor ;)