MrC: While it would make sense to upgrade the cartridge, neither a 2M Red, nor a MP-110(H) would appear to be a really good idea - not only because these would rather be crossgrades compared to the DMS249E (alias Ortofon M10), but also because both would be less ideal for the ULM arm than the DMS249E/M10. And the included headshell of the H version of the Nagaoka indeed would be of no use for you - not only because it wouldn't fit to the arm geometry, but also because of the different connection.
Most convenient would of course be a simple needle upgrade, but unfortunately the needles for the DMS249E, Ortofon M10 and Digitrac 50EP already were the top needles for that family and just on level with the (Super)OM10, 510(II)/VM White and 2M Red, i.e. bonded, medium-sharp elliptical level. However, you could consider what some of the Dual fans, facing similar problems with their Ortofon-made 1st and 2nd gen. proprietary ULM mount cartridges, already did, namely to grab an original or 3rd party replacement needle and have the original tip swapped for a Shibata tip by a professional retipper. Iirc, those guys had that done by Nadelspezialist(.de) for ca. 160 Euro.
Personally I'd rather consider a different cartridge, though. Given that some of the Dutch vendors currently still seem to offer the original SST needle for the GP351 new old stock at a comparatively fair price level, using that on a used or new old stock ELM family (GP330/331/350/351) body/cartridge (half-inch mount version, of course) could be a good idea, if you'd like another comparatively slim and comparatively light "long nose" design, which would look nice on your 3rd gen. ULM headshell, be a good match from a technical point of view (*) and a real upgrade: The SST needle for the GP351 basically sports a moderately sharp FineLine-like tip, comparable to Ortofon's needle 30, but it's nude diamond being round-shanked only (while the Ortofon needle 30 sports a nudie with rectangular shank). One of those Dutch dealers currently also still appears to have a complete new old stock GP351 cartridge (body & needle) for not quite 200 Euro - a good bit cheaper than a new OM30Super, and another plus of the Philips is that it isn't quite as high as a (Super)OM, so you won't have a problem with the tracking angles (SRA & VTA).
Greetings from Munich!
Manfred / lini
*) in terms of compliance as well as cartridge height (as already mentioned above), but due to it's comparatively low weight also regarding the aspect of conserving the ultra low mass approach.