I'm sorry, this is going to be a long post, but Oh, AuntieEleanorsCat I am so sorry to hear how absolutely awful things are being for you just now.
You're actually doing good in making all the arrangements for the future, it's just very sad that you're having to do it from a place of deep sorrow and depression.
I've been bi-polar since I was a young child, and have constantly battled suicidal urges. So I can totally understand and sympathise with how bleak and pointless the idea of carrying on can be.
However, during a long talk with one of the psychiatrists whom I've had over the years he told me of the many, and it was many, tragic results that he'd seen when people had tried to kill themselves but failed while at the same time damaging their bodies so badly that they had no hope of recovery and had in fact compounded their problems.
I also realise that the last paragraph won't stop you if you're determined, but I would love to believe that maybe you might take my unasked for advice, and explore the idea of taking all your pain and stress and worry to God and ask Him to help you find a way through.
I'm not an organised religion person, I have my own personal relationship with God, so I'm not suggesting you become an overnight convert to some religious order, just - please - give God a chance to help?
If you do, I think you'll find that somehow people come forward to offer help and you'll start noticing signs pointing you towards help - e.g., your Social Work department to assist with your son's needs; the Samaritans who'll listen when you need to ugly cry on someone, and your doctor who can relieve a good deal of your hopelessness with the correct cocktail of drugs and referrals to support organisations.
I lost my very much beloved husband to Covid in May 2020, and I wouldn't be here now if I hadn't taken the advice I've just given you. I'll never stop missing him until we're reunited in due course, but I have been amazed and so touched by the amount of kindness, and both practical and emotional support given to me from then until the present by people whom I hardly knew before.
Please, if you feel you're on the edge, and don't want to call any organisation or your GP, then send me a private message and just know that you can let it all out, and I won't try to direct or judge, just sending you love and strength.