Unless there is a very hard requirement for the exact style I think clang-format is a very nice solution. I use it in all projects, even though I don't always like the formatting, the fact I don't have to think about it at all is quite valuable 🙂
I can try to help with the style definition. Though I would recommend letting go of the existing style and simply restyling as close as possible to what you want 🙂 incrementally:
-> touch a file for a change -> first reformat and commit it 🙂