Question Author
Thanks for the additional ideas, all of which are workable and helpful.
Mrs A (helpfully) points out that a few yards from our hallway, where the travelling phlebotomist treats her, is our bathroom (small London flat), in which there is a 'perching stool' which I use for ablutions (one leg), which would easily be moved that short distance down the hall.
Options are great, and we now have many, so grateful thanks for your kindness.
A.