There's still the HD25 or classic Koss stuff (if open-back is ok) being made.
I haven't heard any of these but some on-ear models I am aware of in case you'd find such a list useful:
E-Mu Walnut and Creative Aurvana Live SE variants (*edit*actually I think these might be over-ears, if fairly compact ones). Audio Technica* pro7x, m60x. Beyer DT240. Austrian Audio x15(?). Open-back wise, the Grado Hemp are supposedly decently tuned. I guess worth noting some wireless cans also have wired input (Shure Aonic come to mind, though look to be over-ears).
I always considered the DT1350 a class of its own… generally I don’t like on-ears, so unfortunately I can’t recommend much in the really compact segment, esp not with the quality of the DT1350. HD25 doesn’t sound as good in my opinion. V-Moda XS might be worth checking out.
For open headphones I can second the already mentioned Grado Hemp, which works quite well directly from DAP/phone