I came across this link on another website, I hope it is ok to post it here ...
http://www.geocities.com/grunes/falling.htmlThis is a rather comprehensive document, but essentially it explains how you learn to fall gently. If you watch senior skaters (meaning skill level not age) then you will notice that they tumble often when practicing difficult techniques, but seem to mostly slip onto the ice rather than fall over with a crunch. In essence, I think it is a case of not fighting the fall, but relaxing and sinking into it.
Sorry to hear about your thumb, by the way, I have acquired several injuries so do understand. Hope it is not stopping your skating too much.