Some of these aren’t very straightforward but I don’t think there are many easier ones other than ones like Cy that you’ve already considered
[name_m]Cass[/name_m]
[name_m]Russ[/name_m]
[name_m]Chip[/name_m]
[name_m]Chuck[/name_m]
[name_m]Kip[/name_m]
[name_f]Pip[/name_f]
I think a midle name would open up more options - either nicknames from the middle itself or combo nicknames e.g. [name_m]Cypress[/name_m] [name_m]Michael[/name_m] could be Sim/Cym? [name_m]Cypress[/name_m] [name_m]Daniel[/name_m] could be Cyd/Sid