trans | my trans dad

Hi,
My dad recently came out as trans to my mom and me. Other than a therapist and some online friends, we are the only ones who know. So far it's been a positive experience for all involved, although I have had some feelings of loss. However, I am mostly happy and excited for my dad, who will start hormones sometime soon and plans on eventually having sex reassignment surgery. At the moment, I am still using male pronouns to refer to her, except in the rare event that I use gendered pronouns when it's just me and her speaking, because no one else in our family/community knows yet.

My specific question to any trans parents out there (or children of trans folk) is what kind of name do your children use for you? I am an adult, but I am very hesitant to use her first name, because I would still like to have something that signifies her role as my parent. She has said that I can continue to use "Dad," but I know she would be happier if we could find a name that wasn't male-specific, and I would feel like I'm not honoring her true self by continuing to use it. Mom, or variations of that, don't really sit well with either of us. We're hoping to come up with something kind of unique, so any suggestions or experiences would be welcome.

I would also like to just say THANKS! for allowing me to be part of this community.