I must say, that if you are not already over here and with a withdrawal card, I'd give serious re-consideration to your plans. For one thing, what is your French like, many regions have similar problems to the UK, and the healthcare, though usually excellent, can be very patchy as Lori has said. Very few medical people speak much if any English still one in teh country and outside very large towns and cities. For your situation though, whilst there is improving assistance for Alzheimer's and Parkinson's, that again is patchy, and the number of residential homes with special facilites limited. As the disease progresses language could well become more problematic too. Since Brexit, there are many more considerations to take into account, some of which have been outlined above, and though on the whole we all hope for better weather than in the UK, it cannot be guranteed, as you must know as you have lived here before.
As others have said, the grass is not always greener ..