I tend to agree with @BlackInMind here, but I think it needs more explanation.
What you describe with your left hand sounds very familiar to me. The supination required for classical position on high frets is too uncomfortable to be usable. The left hand wants to be more neutral, which requires, as you say, the guitar neck to be angled upward. But to angle the neck upward, you have to push on it somehow. Classical position does not allow for the left hand to support weight. The guitar must sit in a stable position on its own, without any help from the left hand.
I also don’t like very high slung guitars. Though they do give you a more neutral left elbow, they don’t really solve the supination problem, and I don’t like what they do to my right shoulder. My right hand wants the guitar lower.
So blues position seems to be necessary, because it allows you to rest the guitar on your palm, which means you can push the neck forward and tilt it upward, and put your arm and hand in a comfortable position. But now your fingers are too far away from the fretboard.
Which is what I assume motivates this:
The way I solved the problem was exactly this. I modified my blues position so that the neck doesn’t contact my palm. Instead, it bridges between the inside of my index knuckle and my outermost thumb joint. There’s about 1 cm between the back of the neck and the closest part of my palm. Only the tip of my thumb wraps around the neck. Not enough to fret notes with.
The guitar neck rests there very comfortably, almost like it was made to fit. So this bridge very quickly converts to a grip. I can easily hang the guitar vertically by the neck, by squeezing my thumb toward the base of my index finger. I play single notes in this position about 80% of the time now, only occasionally switching to classical position when I need to reach toward the bass strings or play barre chords. For most other chord shapes, I keep the grip described above.
This grip gives me the benefits of the blues position: I can physically move the neck around and angle it upward for reaching high up the neck. But I can also fully extend my wrist and simply push the neck forward. And my left hand is neutral, not supinated. My fingers are not parallel to the frets, like in classical position. I can bend and vibrato by rotating my left forearm, just like in blues position.
Plus, it has the added benefit of acting like an anchor. Just like my right hand, my left hand benefits from a constant point of contact on the guitar. It allows for more accuracy because there’s less guessing how much the neck has moved in the few milliseconds since the last time I touched it.
Now that I’m familiar with it, I now see this approach as a sort of hybrid classical/blues grip, as it gives the benefits of each without the drawbacks. I also notice it everywhere. Like @BlackInMind, when I examine the left hands of most high-level guitarists, I usually see them using the same grip. If there is any left hand code to crack, I consider this grip to be one of the central concepts, because it solves exactly the problems you describe. It made a huge difference in my playing and my comfort.
). Without any perceived willingness to go away and try all of the above, you are unable to give us any further feedback to comment on - therefore making this issue impossible to cure. All I have left is that you move your left elbow back an inch when accessing higher frets - this might force you to utilise a more pincer like approach with your thumb touching the neck rather than the palm.