You can try Michelle, she pretty much is Julia without her new Luchador moves that come from her forward roll and bridge stance which makes her simpler to use though her potential definitely is inferior to Julia's. But she has the superior mad axes by far because of the okizeme it offers.
But personally, stick with solo until you understand the game a lot better. If you're most familiar with Zafina for now, I recommend to keep learning more things about her such as the moves which catch people sidestepping in certain directions, and the moves you can do against people for okizeme, the setups after throws, the setups after wall combo's, tech traps after juggles, tag assault baits, etc. Until you have a basis on all of things it's best to concentrate those things for 1 character before you have to expand your thought process of the tag launcher, tag cancel system, and netsu management.
But if you are ready, Julia isn't a bad choice. But if you're looking for a tag partner for Zafina that would complement her during tag assault, it's best to find a character with a very strong single hitting move for the TA and finishing the juggle off with Zafina. Julia and Michelle to be honest don't really have that IMO. You can look online for the Zafina player FlyMike and how he uses Ganryu as her partner. It's really cool.
