The chord progression you've written suggests that the E-flat is a suspension in the bass. That is to say, the "real" chord is the D diminished chord (which implies an incomplete Bb7 chord, if we're going back to E-flat, or perhaps a B-diminished 7th chord, if we're going on to C minor) and the E-flat in the bass is a dissonance that is held over from the previous chord and then resolves to the D. What you've written is actually very similar to a super common introductory chord sequence in the Baroque and Classical periods!
Chord symbols of the sort you're using are not that well suited to notating suspensions, especially suspensions in the bass. (Classical musicians have a whole different notation system for this sort of thing, figured bass.[^1])
Fm7/Eb, as suggested by another user, is possible. You could also consider Bb7sus4/Eb. The difference is basically whether there is a C in the chord, or instead a Bb. (You can listen and compare for yourself which sounds closer to what you have in mind. You might also find that you like the sound of Bb7/D better than D diminished, or not.) You could even consider something like writing
Ddim, then add a verbal note something like:
bass: Eb->D susp..
[^1]: In figured bass, you would write an E-flat in staff notation, then put a 4/2 underneath it to indicate that the fourth and second should be played. However, the 4/2 figure is usually taken to imply the 6th (C) as well.