I go along with my sleep doc not knowing what he was talking about ... because the full face mask (ResMed F20) was an absolute disaster... I have high cheekbones and a wide mouth and sizewise am between a medium cushion and a large, with medium just too small and the large way too big. ResMed messed the sizing up on that. I'm desperate for a full nights sleep and went out and bought a Respironics Dreamwear (moves around a lot) and a Swift FX Nano to try. Hopefully one will work or I'll just die from lack of sleep (yes, I'm being dramatic but I haven't slept through the night for close to 6 months and am losing my mind) ...
Hi, my facial features are different than yours but I was also between a medium (too small) and a large cushion (too big) in both the F&P Simplus and the ResMed F20. I went with the large in the F20 because I was waking up with the medium in my mouth. I ended up using a piece of stick-on Velcro and a thin strap from a chinstrap across the bottom of the cushion to keep it down (tiny chin). Haven't used it since I got it to work since I preferred the Swift FX Nano at the time. The trick with the Nano is not to overtighten the bottom strap and make sure the top strap is holding tension on the bottom of the cushion. You want the cushion to inflate, it may feel loose, but you'll know if you get leaks, it whistles or sputters depending on the leak.
As to the hair, I have chin length hair, but thick. I pull some of my hair up into a little ponytail on the top of my head or else use a claw clip to hold some hair up, both of these keep the top strap of the headgear from slipping down my head. I've been sleeping this way for years though, because I was getting so hot and sweaty from the sleep apnea before I was diagnosed.