I don't know if this is going to help you. I just want to tell you you are not alone, in feeling alone. I am 53 and have no best friend. I have felt a misfit my whole life.
I live alone, my friends from childhood are married with children so their time is focused there. My marriage lasted onlyv18 months due to my bi polar that my husband couldnt cope with.
I do have a few young friends from my last job but they are busy with their boyfriends etc.
Like you apart from my mental health issues I have physical health problems. I have had cancer four times and now have some lesions in my back which are suspicious.
I don't have a lot of hobbies but I have decided at this age I have to do something about being alone all the time.
I am joining a book club, and a group for people my age that do many different activities together. Maybe I can make some new friends there.
I wish you well.