Oh dear, poor you and poor, poor father.
My father too said at the same age that he was too old to get another dog, after my mother's death. We saw his point as taking it for walks would have been hard.
Happily, for my peace of mind, a stray cat with a very low opinion of human beings moved into my father's barn that was built in one with the house and lived off the mice he caught there and water from a small ornamental pond.
My father, who wasn't really a cat person, appreciated the help keeping down the mice, so the two rubbed along quite happily. Shadow, as I call him, because he was black and we only ever caught glimpses of him out of the corner of our eyes, disappeared a week after my father died and was never seen again. I rather suspect they are sitting in the hereafter, about three feet apart, carefully ignoring each other.
I hope some nice friendly neighbouring dog trots by and keeps your father company, or a stray cat or a family of birds in his garden, if he has one, can provide a little interest and comfort.