Well, it's kind of like a variation of a service and quality poster I sometimes see in shops:
When it comes to PVs, you can have:
- Small
- Powerful
- Long-lasting
You can pick only two. You can have small and powerful, but it won't be long-lasting. You can have small and long-lasting, but it won't be powerful. You can have powerful and long-lasting, but it won't be small.
From my personal experience, if you are absolutely set on a slim PV, your best bet is to get yourself an 808-base device. Volt, Bloog MaxxFusion, Smoov, Kanger, something like that. All of the 2nd generation KR808D-1 devices (Volt, Bloog, Smoov) are all 5V devices regulated down to 3.6V constant power, and the cartomizers are usually around 2.6ohm, so while you don't get the most powerful vape in the world, it's surprisingly warm and pleasant, and I usually get about 2.5-3 hours out of even the small 65mm batteries. Get a couple of those and a portable charging case and you should be good all day. I personally prefer the Volt or Bloog. They have nice rubberized coatings and work quite well, even the automatics. Automatic Volt batteries are also available in a sealed configuration that all but eliminates the worry of overfilling the cartos. They're not the cheapest kits in the world but they do work quite well.
I don't know if I've sent you my Canadian mod/hardware vendors list but I'd be happy to do so if you don't already have it. It should help you find what you're looking for. I also have a series of 808 reviews coming up shortly (link in my sig) covering the Bloog, Volt and Kanger kits available here in Canada.