Henry Mark, Harvey Mark, Hallam Mark. They're the only others I could think of, although personally to me I feel like none of them have flow and it's because Mark is such a harsh sounding name due to only being one syllable.
@Zöe We have a 3 syllable surname so I feel we can get away with this one ☺️
Harrison and Hudson seems very similar so Hayden for me ☺️ other suggestion would be Hugo