You have to choose a name that matches your own thoughts about yourself. Matilda seems like an old name that is not heard anymore. But maybe that is you. A lot of us try out a name for awhile and realize that it is not us and then come up with a better name. So if that is what you like then try it and see if it works for you.
There are a lot of resources on the internet that can help you access your true gender. Take the time to read them before you discuss being trans with your family. Unfortunately, few marriages stay together after a trans person does that. And remember gender is who you see yourself as and sexuality is who you see yourself attracted to. For instance, I am MTF trans girl that is attracted to girls and sometimes really cute guys. So that might make me a lesbian or maybe pansexual. Don’t worry about sexual attraction at your stage. Thoughts about sexual attraction can change after a time on HRT.
And the resources here on this site can help you also.