Consider those at where your 'not quite forever' ends and what they need, considering those less able and whether it's adaptable if those needs come up. We'd all like to think we'll be fit as a fiddle when the kids leave, but statistically, some won't.
My forever home has a ramp out the front and back doors and has an adapted shower with a seat built in. It has handrails in many important places. It has space for an adapted bathroom downstairs. The kitchen is large enough for multiple to be in there without driving each other crazy (lived with a very tiny kitchen for a dozen years, I'm enjoying the elbow room).
It's a couple minutes from one set of buses and 10 minutes from another set which lead to cities and all of my teens have bus passes so they can travel our area as they wish, giving me some breathing space and them some freedom. The first shop is within about 5 minutes walks, and within 20ish minutes we have several shops including a chemist and banks. We have a big green field out front and woods and walking/cycling paths within sight.
We have a south facing front garden and it's not the big boon many think it is other than it's nicer sitting out there for more of the year. I'm hoping to simplify and add more seating out there. For me, it's more is the garden and home space something you can manage, we've struggled a bit with the garden as we have surprise fruit trees and we bought knowing it will take years to improve much of the energy efficiency in a 1950s all electric house.
As for the kids not having moved out - I already have one lodger, I'm open and like the idea of the others being used for other lodgers or foster children or for supportive housing or as a shared lives carer as long as I'm able, and then in retirement to rent out to some of my friends who intend to continue renting so they have an adapted house as adapted rentals are so hard to come by. Leave the box room for carer equipment or visitors. I live near a lot of bungalows, but really, my house is already adapted and adaptable for most of the benefits. I can only see us moving if all the kids move out fairly far away and my husband and I wanted to move closer, and at the moment I've an adult child who thinks a university 4 hours away 'seems a bit much' so unlike potential infirmity, I find that harder to imagine at this point.