I would recommend getting a 30+ watt regulated mod that uses swappable/replaceable batteries AND that has on board USB charging. The 30 watt IPV mini, Cloupor 30 watt mini, 60 watt IPV 2 (or many others), would suffice.
Lithium batteries are good for a few hundred charge/discharge cycles before needing to be replaced, with mods that use a built-in "proprietary" battery (MVP, Eleaf iStick), once the battery goes so does the mod. With mods that use replaceable/swappable 18650 batteries all you need to do is replace the battery and you're good as new again. I use the $6 Samsung INR18650-25R 20 amp 2500mAh battery
18650 Samsung INR18650-25R 2500mAh High Discharge FLAT Top - Batteries - Batteries, Chargers, and PowerPax Carriers buy them in pairs and always have a new one ready to go.