So I ordered the K550's and have been running through them today. They sound good and are extremely sturdy, but I don't find them very comfortable for more than an hour. They're just too heavy and don't clamp my head firmly enough—though maybe they'd be uncomfortable in a different way if they were tighter. Plus, my left ear is starting to feel irritated from touching the driver cover.
I'm considering sending them back, but as it always is when you live in Ireland, it won't be cheap. I have no idea which ones to try next, or even whether they'd be an improvement. Over the years I've spent a bunch of money on IEMs and have never found one I truly felt comfortable with. I theorized that shoving buds in your ears was not a comfortable experience, so I'm trying headphones. It really isn't any better. It's just a different kind of annoying and discomfort.
Any other suggestions? Maybe I should try some light, portable headphones (HP50, M4U1, MDR-1R, Fidelio L2, Momentum)? Maybe even an on-ear design? Or maybe I should accept that I won't find the right headphones unless I look into open-ear designs?