You mentioned you had tried to grow your mustache out fully, but didn't like hairs in your mouth. I've let mine grow out fully and now only trim the ends every couple of months. The process of growing it out does suck, I'm not going to lie, but as it's growing out use a heat brush daily to sweep the mustache to the sides, from the middle out. After months of doing this the hairs will pretty much stay out of your mouth, even without wax, you just have to train it.
I can see shaving a few hairs off of the top of the mustache, but a lot of guys shave off the top half of their mustache and Ill be mean enough to say it: it looks like 💩 every time. Not only does the edge look oddly artificial, but you see the 5:00 shadow of the shaved part which makes it look awful. Honestly it looks worse than when guys blessed with flawless coverage shave little squares into their lower lip.
Am i the only person who doesn't like the look or feel of a trimmed moustache nothing against people who rock it trimmed just i like the flow of a grown moustache