We've sorted out POA and Wills.
The house is fine for both of us. It's all on one level but we'd would likely need help with the garden if not mobile in future. We've a main bathroom with bath but the on-suite has a walk in shower so sorted that way.
We've shops, GP, dentist etc locally but these are 1-2km away and getting a cab might be hard as we're not in a massive town. Right now we walk, cycle or drive to these places but accept that might need a rethink if both of us were less mobile.
We've plenty of activities locally, leisure centre, library, various community centre type things, swimming pool etc but all that is 1-2 km away. Quite heartened to see folks on mobility scooters going too and from town from where we live. We do also have a bus service past the house but that's relatively recent so not relying on that in case the route changes again.
Personally if I'm the last one left I'll likely look for a smaller place closer to a slightly bigger town. We may do that anyways especially if one of us couldn't drive.
Both of us will pay for whatever help we need. We've no kids and even if we had we'd never ever ask them to support us in old age.
We're both very fit, do lots of exercise, daily walk whilst WFH, monster hill walks at weekends. I do some strength training - being at the age where the hormones go wonky I want to keep what bone mass as strong as possible. We've lots of mates a lot older that are still very active and we can see very much the benefits of use it or lose it.
I'm also quite determined that if given a diagnosis of dementia or similar that I will (assuming I'm capable) take steps to ensure I won't be around too long - a long walk some place I won't be found perhaps. Dignitas or similar might be an option if I'm diagnosed with something terminal or insufferable but unless things changed I don't think you can yet go to Dignitas with dementia. My biggest fear is I develop some cognitive impairment and I'm no longer able to take action or decide for myself what I want.
My DH is aware of my wishes with regards to medical treatment in such circumstances or anything else where quality of life is gone - basically pain relief and nothing else. I do really need to write something to give to the GP on this.