Perhaps theres just not enough Nicotine in your juice? If you're
vaping 12, try 16, or 18mg/mL.. If you're
vaping 18, give 24 a try. That could be a cheap way to get the satisfaction you're looking for, if not, VV mods are a great option..
The Lavatube is a fine VV device for the price.
The benefit to a true "Buck/Boost" VV device, like the LavaTube, and ProVari (it can increase, or decrease voltage over, or under that of the battery feeding it) is multi-fold.
1) With a single battery, there's significantly less chance of mis-matched "stacked" batteries going into thermal runaway, and
2) A full range of voltages will open a whole new world of trying different attys / cartos, and driving them just so, to get that "sweet spot" of vapor, TH, and flavor with your various favorite juices.
The ProVari, and Darwin are 2 of what some would call the "Gold Standard" of VV devices, but they're both pricy options.
Once you have expanded past an eGo, Variable voltage is a great next option. For the $60-$70, I'd go with the Lavatube. The ProVari ($160-$300, depending on finish) will give you more useful information about your atty resistance and battery state (testing each while under power) and the Darwin ($230 last time I checked) will allow you to dial in a specific wattage (heat) and lock it there.
There are a *ton* of other options out there as well, these are just the ones I've played with.