I don’t think there’s any particular “best sub” for this.
TBH, I still smoke, and like you there are many reasons. I think each person’s situation will be different because there are different levels of habituation.
For me, smoking often becomes an excuse to get outside and have some fresh air, and connect with nature. The idea of “smoke break” is a thing that habituates a lot of folks, especially if it’s a social thing at work. I think because there have been several long periods in my life I’ve done it, as well as knowing other people who do it who I’m social with, me attempting to give it up would be different to, say, someone who has only done it once, for a few years.
There are definitely techniques though. One of them (not a doctor so do your own research) involves taking supplements that reduce the nutrient deficiencies ordinarily caused by smoking, especially flushing niacin. The other, which I kind of like to do anyway sometimes, is delaying your lighting up through other enjoyable activities performed in the same place you ordinarily light up, so you can change the association. Or don’t immediately try to quit, but try to smoke with full conscious awareness of the process of smoking and body awareness. This is an interesting one, because if you succeed you’ll often find yourself coughing and that will lessen the positive association with the act.
Yeah, the other sub suggestions people have given are cool too. I don’t have anything else to add there.