If you dont want to spend a fortune but you want have some ability to expand into devices that need more watts....
Look at the Eleaf Istick 30watt. The new 30watt addressed the complaints about the 20watt. Mainly adding a stainless steel spring loaded 510 connection. The Nautilus should fit and run nicely on the Istick 30watt. It ran fine on my 20watt but the signal is not as smooth as the 30watt (according to
reviews). It will also fire down to .4ohm if you ever care to venture into sub ohm devices like the Atlantis or Kanger SUB Tank.
Hard to beat for sub $40.