Using scale property to change size worked for me.
Add these lines to your <switch/>
tag in xml file.
android:scaleX="2"
android:scaleY="2"
You can change scale value as per your need. Here value 2 makes it double in size, similarly value 0.5 makes it half in size.
Example:
<Switch
android:id="@+id/switchOnOff"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:scaleX="2"
android:scaleY="2"/>