A couple of other options:
If you can find the old version of the Teva Terra-Fi sandal (the ones before the current model, hard to find now), they provide more support than Superfeet insoles and may work for you. The current model is OK, but not as good as the previous ones.
Chaco sandals have a shaped footbed, approved by the American Podiatric Medical Association (APMA). More info at http://www.chacousa.com
They feel very different to all the footbeds and orthotics I've tried. I've not used them on a serious walk yet, but they seem VERY good so far and do something that nothing else I've tried can do. With every other footbed I've used, my right foot lengthens (pronates) when I put my weight on it. Superfeet help a little, Orthaheel footbeds help more, and it is still noticeable (though much improved) with full custom orthotics. With my recently acquired Chaco sandals, however, this doesn't happen at all!
As a matter of interest, Chaco also make replacement footbeds for boots. I'm dying to try a pair, but they only seem to be available in the USA at present :( If I manage to get hold of a pair, I'll report back on this forum...