Best formula to switch from breast feeding

PLEASE NO BASHING. I have my breast fed my daughter since she has been born, so 3 straight months. I am no longer on board with it, I am just exhausted all the time, and I can't get myself to agree with myself anymore (that make since) mentally I want to keep going because it's best for her but physically I just don't want to anymore... I know it's my decision and as long as she is fed and healthy that's all that matters, so I guess my question is.. WHAT is the best formula to switch her over to and WHAT would be the easiest way to make that switch??