Some options include:

ACT Dry Mouth Lozenges with Xylitol
XyliMelt tabs

I have become a mouth breather because the muscles don't keep the mouth closed naturally. I use a VPAP breathing machine with max pressure of 24 cmH2O because breathing stops and the body can no longer react to CO2 buildup in the lungs. Most CPAP type machine users max range of pressure is 8-14 cmH2O. When it ramps up to try and kick start breathing it can almost blow the mask of the face or if I use the nasal mask it blows the mouth open. I use a ResMed Adjustable Chin Strap. It goes across the H&N and top of the head and holds your mouth shut. I use it with out e machine when it is real dry.

Go buy some type of RH gauge and keep it near the bed. When we hit sudden extreme cold temps, RH drops over night from 35% down to 15%. Those nights or all nights in winter require a cool mist humidifier near the bed.

It took many years to get to this point but I can sleep 8-9 hours without any issues. In the morning it is a "chore" to clear out all the pooled secretions, clean the tongue. During the evening it takes some effort to ensure the nasal passages are clear for nighttime breathing. I get thick secretions so I have to manage that so I don't get big thick plugs stuck in my voice box area as they shut down breathing.

This may help.

SCC Stage IV, BOT, T2N2bM0
Cisplatin/5FU x 3, 40 days radiation
Diagnosis 07/21/03 tx completed 10/08/03
Post Radiation Lower Motor Neuron Syndrome 3/08.
Cervical Spinal Stenosis 01/11
Cervical Myelitis 09/12
Thoracic Paraplegia 10/12
Dysautonomia 11/12
Hospice care 09/12-01/13.
COPD 01/14
Intermittent CHF 6/15
Feeding tube NPO 03/16
VFI 12/2016
ORN 12/2017
Cardiac Event 06/2018
Bilateral VFI 01/2021
Thoracotomy Bilobectomy 01/2022
Bilateral VFI 05/2022
Total Laryngectomy 01/2023