For the smaller batteries, go with regular resistance Boge cartomizers. Dual coils can be used on an eGo but it's awful hard on the MOSFET switch inside the battery...just wanted to let you know this. A bunch of people use them on the eGo but it's a risk. If the MOSFET switch goes up, your battery is dead and unusable.
If you need to cut your mg down on your juices, buy the same kind in a low nic and pour them together. This cuts your nic down to a different level. Example: 24mg (which you have) + 12mg (you would need to buy) = 18mg (if this is what you are trying to achieve). If you cut them down by just adding unflavored pg or vg, you are going to loose the flavor some.