Does anyone haves any ideas of female spellings of male names like Johnnie and Brianne?
You can always do bigender/androgynous names like Monroe, Alex, Sam, or Danny/Danni
A good resource would be baby name websites like Nameberry. Its where I got many of my character's androgynous names! Nameberry also gives other spellings when you click on a name, so its a good source. Hope this helps!
There's also a site called fantasynamegenerators.com, and its honestly a fantastic tool for naming literally anything not just characters. You can even get descriptions for things if you're really stuck.
