Hi and welcome. I have seen several recommendations for the iStick 30 and the Cool Fire 4. Both of those are excellent choices for a beginner. If you want removable batteries-- I prefer them-- then the Kanger Subox kit is a nice place to start. You don't need tall power on a Nautilus. 15 watts or so will give you all that tank will handle. If money's no object, buy a Provari. US made, warrantied, and they can be serviced. Really, they're about as good as it gets for low power applications. Their P3 is a 20 watt tube, and the Radius is a 40 watt box.
Temp control is another matter. The problem with most small mods in TC is they only support Ni200 wire. Both the Titanium and Stainless wires offer better flavor and, I believe, better all around performance. If you want to future proof, the best buy right now is a Wismec Reuleaux RX200, which is way more power than you need, and supports SS wire, and has upgradable firmware to keep it current. It's larger than you want, probably. It's a very small 3 battery mod, but it's still 3 batteries and that's a fist full. Another solid choice would be a SX mini. The new one is supposed to support Ti and SS.