Once you're up to dual 18650s, small is going to be a tough order. You could also shop the newer 26650 mods that are appearing. Go big or go home!
Depending on your circumstances, you could also rock a mod with a usb port so you can vape as your charge. For example, my cloupor will last me my longest workday--but if it didn't, I could just jack it into a computer or wall charger. With that in mind, focal has a hana mini clone with a replaceable 18490--not as good as the standard cloupor but better than the
fasttech lottery. Throw on a coupon code and you can have it shipped for $40. IVP2s is another nice one with usb recharging if you need more watts, stepdown and have a larger budget--$120 or so.