[name_f]Tess[/name_f] works as a stand alone to me! It feels substantial and well-established! I think you’ve got so many brilliant suggestions already but I’ll throw in:
[name_f]Tessan[/name_f]
[name_f]Ottessa[/name_f]
[name_f]Anastasia[/name_f]
[name_f]Constance[/name_f]
[name_m]Tennyson[/name_m]
Tessiana
Teska
Tesnim
Tessibel
[name_f]Astraea[/name_f]
Some of these might be stretchy though