It can be very hard for some people to ask for, arrange, and accept help, other than from family. I am physically disabled and my husband, age 77, has early stage Alzheimer's. We would have a much harder time in our apartment if I could not hire helpers to do things for us that younger, abler people can do themselves.
It is probably easier for me because I had a business once for which I hired employees, I supervised college and graduate students, and I have hired home helpers a number of times. Some of my experience was just trial-and-error. I assume if you had a home helper their pay would come out of a social service agency.
I know some elderly people who have a home helper. They frequently complain their worker comes late. Other than that, they don't seem too unhappy with the arrangement.
I think the most desirable outcome for you, Sarah, might be a subsidized (low-income) apartment in a building that is reserved either for elderly or disabled tenants. If you look at "market rate" apartments in your area - the rent that everybody else has to pay - they will probably seem out of your price range. But subsidized housing is more affordable. I don't know how systems vary between Canada and US, but it seems from things you have said that there is something similar there.
A low-income apartment and a home worker from a social service agency might give you a pretty good quality of life. The worker could help you with laundry, paying bills, tidying up, and other household chores. Although you might have a hard time imagining it, many of the things you rely on your parents for could also be done for you by a paid worker.
There are good and bad group homes, but in all cases, you would have to be able to get along with other people in your living space. Would that be easy for you? You mentioned people moving out all the time from the boarding house. That is probably less true in a subsidized building and a group home, since it takes so long to get into one.
I've mentioned my concern with the rats before. I still think you should contact health authorities for your city or county and make a complaint. It doesn't sound like the trapping you tenants have been doing is controlling the problem.
I think you can make a better decision about your future if you tour some group homes and also some subsidized housing. A social worker should be able to set that up for you. Best of luck.
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A finger in every pie.