First of all, yes, I think just focusing on the breath is a good idea. Please do so. I'm just going to say some things that I hope help you.
That having said, I acknowledge the landscape of the jhana teachings is quite a mess, and it's quite sad really for it to be this way. But in my eyes it can only mean, jhana is not easily achieved, it is rare. If it were common, there wouldn't be so much different opinions.
But the way this landscape is, is not a problem if you have faith in a specific approach. And I think your problem is, you do not have such faith in a specific teacher or teaching. That's good for it keeps your options open, but as you noticed, it can also become a bit of a problem. I really want to help you, not hurt or confuse you even more, so don't take this the wrong way, but perhaps that lack of faith is because you may actually not have achieved a jhana? Because, before the Buddha rediscovered the path, he recollected his jhana experience as a child and immediately knew, that yes, that's the way towards nibbana. So I personally understand jhana to be so powerful, they should give us a similar faith of "YES, this is the way". If in certain systems you experienced "this and that jhana", but gave no such confidence.. maybe reconsider if that's the right system for you.
Again, I'm very sorry if it makes you doubt even more, but perhaps this can help. With all respect, I think you are very well on the path and a very skilled meditator already. But here are some other perspectives that may help more:
Instead of focusing on the jhanas, how about focusing on what keeps the jhanas from arising? I'm talking about the five hindrances here. If a teacher can give a good explanation of the hindrances - why they arise and how they prevent jhana, and also, how they relate to the rest of the path (and nibbana), I'd say that's a teacher to follow. If a teacher fails to explain to you how removing specific hindrances relates to specific states of meditation, that may not be a good a sign. I mean, we are often without the 'worldly' version of sensual desire, anger, restlessness, sleepiness and doubt. For example, when we are taking the car for a drive, when we are painting a wall, things like that. Does that make it jhana? No, of course not. Everybody who drives a car would become enlightened, which obviously is not the case, just look at how some people behave in traffic
. So the hindrances must be something very specific. A teacher failing to address this, in my humble opinion, may not really understand jhana either.
Or how about forgetting jhana in another way, by steering the mind directly towards nibbana? I don't know if you have the courage or the insight, but if you do, you can also bypass all interpretations of jhana. By its nature, the path will take you through them with this approach. This is another way of saying: just let go. But it takes a mind that is willing to give up its own existence. This was the Buddha's instruction also, to paraphrase: "A mind willing to let go will achieve samadhi." It just will. Just keep letting go of everything. Of ideas of jhana, thoughts about jhana, of "you", off "you" controlling anything, of the mind, of consciousness, of everything. And by that nature, it must go the right way. Whatever jhana is, by letting go, they will come. The Buddha promised this.
Please don't take this the wrong way, not as me correcting you, or anything. I just hope you can find some insight in this, however small. It may just be the tiny change of mind that you need. If not - please be willing to ignore this entire post. It's not easy to find the right words to say to people when communicating only by text.