I had the same problem. My name didnt really have a masculine counterpart. It was Maggie.
I chose Elijah, for a few reasons, 1. i went online, posted my picture and asked people what my name should be, I got Elijah, and then I got a lot of people who agreed with that.
2. I love the name Elijah, it isnt too rare, but not too common, and it is a pretty name I think, and I am not an extremely masculine guy, so it fits.
I would suggest that you and your guy go to a name website, think about what letter he likes.. for me. I always loved names that started with E, hence Elijah. Then just have fun looking through the names, and once you find some, test them out on him, call him by the names and see how each of you respond to it.
A tip... names will always feel a bit weird in the beginning, someone will call you by it... and it wont feel like its "you" you just have to get used to it... ever sense I switched to Elijah.. the name Maggie has completely disconnected to me, and its hard for me to respond to it.. its an interesting experience.