Well, he smokes Ultra Lights which usually are .8 mg of nicotine per cig. I was a pack a day Camel Filters and 24 was good for me. Plus, its WTA which usually packs a bigger punch.
I do have some 24mg left, you think I should refill with that?
You can mix equal amounts of 12 and 24 and end up with 18, stuff like that.
How much nic he needs is a decision he needs to make. IMO, the biggest part of a successful smoking-to-vaping switch is getting juice that is "right" for that individual.
You can give them an ego Twist or Vision Spinner, add a Protank, and that will do the job as far as hardware. No, it's not as nice as a Provari, but it will get the job done, and it will do it for everyone. But juice, they need a flavor they like, and they need the right nic level. Not too much, and not too little. (I'm trying to avoid a Goldilocks story here, but it's hard.) The "right" juice varies, both in flavor and nic level, quite a bit from individual to individual.
The part where he is "sort of complaining that he really wants a cigarette" makes me think "he needs more nic".
I started at 24 and it wasn't enough. I had to go to 30 to get off the cigs.
But I think the big issue here is it doesn't sound like he wants to quit smoking. I don't blame you for trying, or for telling him "I'll help you vape, but I'm not buying you cigs". But I'm pretty convinced that if they don't really want to switch, it won't work. I've bought starter kits for several people, and taken them to the vape shop to pick juice which I also bought. None of those made a successful switch. They tried it, and they still vape now and then in places where they can't smoke, but that's about it.
Even if he doesn't make the switch now, and goes back to smoking as soon as he gets some cash, it's possible that he'll come back to it later. Good luck with it.