Quick overview of my mum's situation.
We moved about 80 miles away from mum when she was in her late 70s. Not because we wanted to leave her but because, for our new born DS's sake, it was the best thing - out of an area of London that was seeing more and more knife fights in school, etc, etc,
Anyway, mum hit 80 and decided she liked the little market town we live in when she'd visited us a few times. She lived in a council flat and we were lucky enough, after 2 years, to get a transfer to a flat in sheltered housing. She'd always poo pooed sheltered housing as being 'for old people'! She absolutely refused point blank to live with any of us - she 'likes her own front door' according to her.
She moved into her flat, about 10 minutes walk from me. Six months later she had a heart attack (not brought on by the move - she was incredibly happy about moving). it took six weeks after leaving hospital before she could be left completely alone - I had to do a daily walk with her to get her fitness back. Couldn't have done that if she'd have been at the original flat 80 miles away.
Fast forward a couple of years and she was diagnosed with Alzheimer's. She is still living in her flat - my sisters, DH and I cover her appointments, finances, shopping etc. She got an attendance allowance which we currently spend on a weekly cleaner as we couldn't keep up with her cleaning on top of everything else (all of us have young/teenage children and work part time - DH works full time but often from home which helps).
Her living in sheltered housing (and going to her Day Centre once a week) has helped her a lot. She goes down to the communal lounge each day for a cuppa and a chat - does puzzle books etc with her friends. They keep an eye out for her and knock if they haven't seen her each day. The warden (who is only there in the morning Monday to Friday because of cutbacks unfortunately) organises sing song nights, bingo etc., they had a party there and at the day centre for the Queen's birthday. It's all helping her feel less lonely.
I still get the phone calls saying so and so hasn't turned up (she rang on Sunday saying her cleaner was late - she thought it was Monday) but I don't get the calls for a 'chat' three times a day any more. She has her friends for that which is great.
Mum's block is being redeveloped and they are moving everyone out soon. Mum's lucky enough to get a place in an 'extra care' sheltered scheme - they have 24 hour carers in place on site but each person has their own flat and takes care of their day to day lives. Mum can't wait as they even provide a 2 course hot meal each day (for a fee of course) and mum's now 'getting bored' as she puts it, with cooking. She won't be going back when the old block is finished - her needs have changed.
I'd say sheltered housing, attendance allowance used to buy in care or domestic help (you probably will get it if she is diagnosed with dementia), a good day centre and try to move her closer to you (or another member of the family) so you're not running about like a headless chicken if there's an emergency are the key things. Mum wants and needs her independence and I need my space. I still get driven to distraction - appointments or problems always seem to come when DS needs me or I have a busy week but that's life!
Mum said to me, just a few weeks ago, that moving into sheltered housing was the best thing she ever did - she doesn't have to time to get lonely anymore. Which is a lovely thing to hear.
By the way, if you do get a diagnosis of dementia or Alzheimer's, ask about the Admiral's Nurse service. They are specially trained to support you and your family whilst you work out what you and you DM need and they can point the way to other services (my one was the person who helped us apply for a Blue Badge - which we got).