I have low and steady pressure, with a max inspiration of 8.5 mm/H2O. So, I can afford to leave my strapping looser, but it does mean more leaks when deeply asleep. So, I learned to sleep on my side, almost exclusively, and to fold my arms, and my wrists, and tuck my hands on either side of my face, close to the mask. This might sound weird, but it actually prevents all but the most egregious of leaks. Most importantly, if you get little puffs and noises that alert you as you're trying to fall asleep at bedtime, this is detrimental as it tends to go on until you fall asleep out of plumb good luck. The bent wrists, with the backs of my fingers against my cheeks and chin, is something you'd have to get used to, but it works really well. It provides a bumping post of sorts against whichever side of your face the pillow is supporting, and prevents displacement or distortion of the seal by the pillow material. Might be worth trying it. If it works, you can loosen them straps a smidge.

Try the Barriere Cream. It works very well for pressure/contact sores and welts, and for 'contact dermatitis.' My wife steals my tube all the time because she learned that it works well for her needs, and she's very finicky about stuff.

As for better filters, the ones they provide are good, but they're not 'HEPA' variety. I think you can find them, but I have no links as I seem to be fine and have never sought them. Or, look for a material of that nature, with about the same thickness, and simply cut out from a sheet of that material what will fit properly and do the job.