Thanks for all the replies, which I've been reading and applying with interest. I have a pair of slippers that lace, made of suede, that have NO sole other than a thin layer of suede. I've been using these to train in since reading the first reply. Yes it still hurts, but from a 3 minutes-to-pain start I'm now up to 15 mins before it hurts. Proving it's muscular pain. It doesn't cramp, but feels very similar to cramp pain. Luckily I don't have any issues with my calf/leg as I'm a devil for walking barefoot at home all the time. That doesn't hurt my foot, but standing for any length does. I once tried Tai chi and had serious arch pain doing that.
foot exercise wise, I'm struggling to do doming. It doesn't feel or look like anything is happening unless I scrunch my toes. I am spending time each day scrunching a towel with my toes so hopefully that'll help. So far I've been unable to pick anything up with my toes, but I keep trying.
Thanks for all your suggestions
Lesley