Cat Vomiting - please help

I have a 13 1/2 year old male tabby. About four months ago he started
to vomit usually, but not always shortly after eating. Since I only
feed him once a day that meant he threw up all his food for the day.
Right after that he'd be begging for food. I took him to the vet who
examined him and said he appeared to be just fine. He suggested it
was probably a hair ball and told me to give him hair ball remedy
twice a day for a couple of weeks. I did but that didn't help too
much. I tried feeding him very small portions many times daily. I
even tried tossing the food on the rug to force him to eat slowly.
Nothing really helped. Eventually the vomiting stopped on it's own in
a few weeks.

After having no problems for about two months he's started again. He
threw up his dinner yesterday morning and this morning. I feed him at
8 pm at night but when he threw up it was clearly his entire meal.
Since he sleeps right after eating for the rest of the night I'm not
sure if having the whole meal still in his stomach is unusual or not.

This morning he not only threw up the meal but continued throwing up
for about 15 minutes. He threw up 18 times in all. He has NEVER done
that before. About 15 minutes later he was begging for food.

Here's my problem: my husband just had heart bypass surgery. I am
barely able to cope with what I need to do for him. I cannot take the
cat to the vet and start with tests, special treatments,etc. In fact
I can't take him at all. If he doesn't improve I may have to have him
put down since I cannot allow the cat to interfere with what I need to
do for my husband. There is nobody else that can help me with the cat
or my husband.

I love my cat and don't want to lose him. I was wondering if I should
change his food? I give him Science Diet Feline Light Maintenance
(1/2 cup daily). This has been his diet for the past 12 years and he
has thrived until now. Is canned food easier to digest? I just don't
know what to do.

Don't know if this is related but a few days before this all started
four months ago he ate a mouse. He caught it in the kitchen, ate it
and threw it up, along with his food all over the house. It looked
like a mini autopsy on my living room floor. The vet didn't think it
was related.

He is an indoor cat and has no contact whatsoever with other animals.

Any suggestions would be greatly appreciated.