A quick update. I ordered the green Specialized Body Geometry SL Footbeds. I found they were a little too high on the arch support so exchanged them for the middle ones, which are the blue ones. These felt much better. No arch discomfort during this morning's ride. They fitted perfectly into my Fizik X5 Terra shoes (which are actually SPD shoes and not SPD-SL, although they are shaped very much like SPD-SL shoes).
Feet feel more snug in the shoes.