But eventually settled for this
This is probably some of the oldest fabric in my stash. When I was 12, all the girls had a term of sewing lessons (the boys did woodwork or metalwork or something like that) and we all had to make ourselves a wrap-around skirt. This is the fabric my skirt was made from.
I ironed it.
Then I cut out a piece of kitchen paper to the size of the top of the shoe. I thought of using paper, but found the kitchen paper easier to fit around the shoe to get the shape.
Then I cut out two pieces of fabric allowing about 5 mm extra all round, put glue over the surface of the shoes, stuck the fabric on, smoothing it as much as possible (I had my foot in the shoe for this to keep the shape) and left them to dry.
Then I folded under the front and back edges and glued them down, and trimmed the side edges.
What do you think? I'm going out for lunch tomorrow, so may give them a test
I'm toying with the idea of adding a bow ...
... or maybe a strip of ribbon ...
... but I've not decided yet.