Hi
I hope i am not too late in responding to this but it may help for the future.
I use Sodium Bicarb Mouthwash. It help to clean all the dry and yucky crap from the tongue, cheeks and gums. Use it as often as you like.
For the ulcers which are from low immunity and are like a type of thrush or other infection, get the doctor to give you a script for Nilstat Drops. They work really well and really quickly to kill the infection and stop the symptoms.
Between these two things, and brushing every day, your mouth should be ok even when chemo, radiotherapy and low immunity try to make things miserable inside your mouth.
Best wishes
Ash