The dry Brut options are better than the sweeter Sec or Doux options. So many cocktails contain sugar syrups, and as such are extremely tricky. Some of those syrups are available sugar-free, but I haven't seen any of them in bars. It might be easiest to stick with a decent very dry champagne or white wine, or have your night and get back on the horse tomorrow. You only have one birthday a year, so it's your choice.