Have you looked into xylitol? I also have a dry mouth and have been using xylitol for a few years now. Wouldn't go without it.

I mix 3-4 TBSP xylitol with 1/2 cup hot water (using a kettle) to dissolve, and then fill the 12 oz bottle up with cold water and refrigerate. I add the essential oil I feel like (peppermint, spearmint, eucalyptus, tea tree), although those may be off limits if your mouth currently has ulcers. They could burn. Each day I fill a small clean spice jar up with some and leave in a corner of the counter and take swills throughout the day. It is important to swill the entire mouth so every nook and cranny gets moistened. If it has an essential oil, I then spit it out. If it is plain, I can drink it down if I feel like.
I keep a sippy cup at the top of my bed, and take a sip, swill it around and swallow it down every time I wake up. It is habit now.
I never let my mouth get dry.

I don't get cavities, which you are prone to with a dry mouth, and I also don't get plague buildup, although I do go to the dentist regularly.

I even make my own xylitol mints. Simply heat dry xylitol on low (3-4) until it melts and gets kind of clear and add essential oil if you choose. Pour onto parchment paper or silicone and spread to desired thinness and once hardened break into bite size pieces. I keep a small container of these in my purse. Or you can buy xylitol mints or gum. Walmart has xylitol gum in the aisle as you are going into the self checkout.
If I sound like a bit of a nut case about xylitol, it is because I am. It has been transformative for me.

Google xylitol and teeth. There is lots of info.
Here is one site: Just a moment...

Another thing you could do is ask your compounding pharmacist if it is possible to get unflavored lidocaine mouthwash, if that would help with the burn.

I bought unflavored lidocaine with Maslow on Wednesday. It works to numb my mouth. Thanks for the info on xylitol. I’ll have to try it!

I buy my xylitol from Amazon. It looks and tastes like sugar. It is a sugar alcohol which some people's stomach's are sensitive to (gas, diarrhea etc). If that is the case, spit it out during the day, and only swallow it at night rather than get out of bed. The small amount ingested at night shouldn't bother you.