Hi Max's Mum. Thanks for the suggestion of the Merrel barefoot shoes; I've already got minimal - Vivobarefoot (Terra Plana) Neos (noraml and trail), which I'm really happy with. But everyone keeps telling me I need more cushioning for the 50-miler, and I'll admit that the balls of my feet were quite pleased when I switched from Neos (normal, not trail) to more cushioned shoes after 15 miles of road running last Saturday.
I do have a pair of the Neo trail one size too big as well - suppose I could try those with an extra insole???