There are some things to try for dry mouth. Rinse with Biotene before bed (I prefer ACT Total Care Dry Mouth Rinse) but both are good products.
For mouth breathing, the “soft” cervical collar has worked for many here. Also keeps you from tucking your chin to your chest. It’s important to measure the circumference of your neck and add a couple inches. Also measure for height, from chin to neck, then subtract an inch. The collar works best if not worn tight.
The “tongue suck technique” has been around for quite a while now.
It takes practice and commitment to master this, but well worth the effort if you can. I used to use a chin strap and hated it. Learning this technique gave me the pleasure of throwing the chin strap away.
Tongue Suck Technique:
Place your tongue to the roof of your mouth with tip of tongue behind front teeth. Slowly suck upwards and back.
This places the tongue in a natural position, with the back of tongue sealing the back of the throat so that if you open your mouth/jaw while sleeping, no air will escape.