I'm sorry this is so hard. Despite having, and having had, very old pets with similar and their own problems it's still not something someone else can really advise you on.
I think I found deafness to be worse for my old Lab girl than her very bad, arthritic back. She couldn't hear our concern and was startled by sudden appearances. We tried to stomp on the floor because she could feel us coming but it didn't always help.
Right now we have a 16 year old cat who is stone deaf and it doesn't seem to bother her at all. The 20 year old cat is nearly as deaf but dementia makes her life, and ours, much more difficult. She does the deaf cat howl. She also has worsening arthritis.
Rescue Remedy does help our 29 year old cat at night, a bit. If you ever want to try it be sure to NOT use the candies because they contain xylitol. It's tempting to use the candies for many dogs as they just gulp them down. Don't.
I am interested in the homeopathic sleeping aid you mentioned. Can you give the name of it?