They now have a DM250 version - https://www.kingjim.co.jp/pomera/dm250/
edit: Actually this seems to have an LCD screen like their other models, rather than the DM30's e-ink, which is a shame. Still, it might be better than the alternatives.
Since you seem to know about these things, do you have any suggestion(s) for where to buy a DM250, preferably with a US keyboard layout? Somebody elsewhere in this thread said that exists, but I couldn't find any mention of it myself.
Amazon JP will start shipping the DM250 at the end of this month. The device only has one keyboard option as far as I know, but it comes with decals to switch it to a US layout. The layout is a bit weird (e.g., the enter key is split in two, which both perform the enter function) but probably ok, I'm guessing.