Here are the results of my double digging this far. You can see the difference double digging makes. The bed on the left has been double dug twice now and has fewer clumps and also holds water much better, as indicated by its darker color. The one on the right has been double dug for the first time and is clumpy heaven.
This bed has been double dug several times and is easy, comparatively. I've spread compost over the bed before digging.
In total, I spent 1 hour and 20 minutes double digging today. I've only completed 1/3/ of this long bed, but I shall persist.