Even so, some people have had success using nasal splint devices that you can get at most drug stores. There are two types, external adhesive and internal. I prefer the internal since the adhesive of the external ones irritates my nose. The ones I use are called Sleep Right and I get them from Walgreen's, 3 for $6. They allow me to breathe exclusively through my nose without any distress or discomfort. I use them along with my full face mask and never have any dry mouth issues. I rarely need to use the humidifier except in cold winter months when the furnace is running.
I also use Nasacort daily to keep my nasal passages open as much as possible. It's approved for daily use and year around if needed. My ENT doctor approves of using it as needed. It works great for me where other nasal sprays have failed. Beware of any nasal spray that cautions against using it for more than 3 days. Those types will do more harm than good.
I have used a full face mask for over a year now but have just this week started testing a nasal pillows mask. So far I haven't mastered the mouth leak problem but I sure like the comfort it gives as opposed to the FF mask. I may have to resort to the mouth taping method since I've tried every trick with tongue blocking and it fails as soon as I get close to falling asleep. A chin strap doesn't help since the air goes right out by blowing my lips apart even when teeth are clenched together.
The reduction of the pressure range on APAP is a good start, stay with that and if you must change to a higher pressure, change both the low and high settings accordingly. Consider this: There is no sin in running the pressure below what is required for therapy. If you have to do that to allow you to buy time to get acclimated to the discomfort of the therapy, so be it. That also allows you to slowly inch the pressure back up when you inevitably find that it no longer bothers you. That also allows you to get the leaks under control and master fitting the mask to minimize leakage so that eventually you can make it work at higher pressures. All that comes with time and effort.
Of course the nice software you get here will be very useful for checking the effects and measuring progress as you go forward.
I hope some of this helps you. Good luck with your quest for relief. Keep trying and you'll find what works best for your particular case.