Wondering about formula

Hi I currently breastfeed my 12 week old and she eats great and I love it. But she doesn't sleep more than 2 hour stretches. People keep recommending formula which seemed crazy to me since we breastfeed fine. But I'm so tired that I'm considering just giving her a big bottle of formula just before bed. Maybe the big meal/ not as easy to digest formula will help her sleep a little longer. What do you all think?