I would definitely ring up a few local animal charities (or contact them via Facebook) as there are indoor cats which might have medical conditions that charities agree to pay for their medical bills for (they often have a deal with a local vet) if you like animals, they do give you so much joy and companionship.
Definitely try a choir session or two to see if it would work for you, you are obviously musical.
Have you looked at 'Meet-ups' ?
It's an online thing where people set up their own interests groups to get people together who might have similar interests (not dating) so for example there might be a Theatre group which organises trips to see shows. There might be a few you are interested in locally?
Would you be interested in joining a Church/faith group? Not my thing, but I have lots of friends and family who are members of a church and they get so much support, friendship and community from belonging to one.
You are so young, I know you must feel worn out and slightly defeated from your health conditions, but there have been some great suggestions on this thread, which might not all be right for you, but giving new things a go is half the fun.
If money is an issue there is a long-running thread called '£10 per day' (I think in the money section) which has lots of ideas about earning money mostly online, from home. I know you can't do too much repetitive stuff, so might not be right for you, but you might be able to do small chunks like surveys at a time?
Again thinking about earning money to help pay for all your new activities, could you babysit? Where I live there are various local WhatsApp groups (neighbourhood watch etc) which you might be able to reach out advertising yourself as a babysitter? It would get you out of the house and connecting to other people and earn you money? There is a website called 'sitters' where you can register. I don't think babysitters need to be Ofsted registered etc, unlike child minders? With your experience and your crb you would be a great babysitter, and it's usually not physically tiring.