I ordered a pair (via Zenni, just some regular polycarbonate lenses) that are at just the right optical power such that if I fully relax my eyes, objects 1 metre away are in focus. When my monitor is that far away, it's at optical infinity and very comfortable to look at for long stretches. It's a very noticeable difference: on the occasions that I forgot to put the task glasses on and wear my normal glasses by mistake, my eyes almost always end up feeling sore after a few hours.

I'm tempted to get another pair at 50 cm for laptop and phone use.