Breastfeeding and formula

Stacie • Mother to Ben 👦🏽, Bash 👦🏽, and Braxton 👶🏽, 420 enthusiast 🔥💨, lover of life 😍🤘🏾
If you know you're gonna be breastfeeding, should you invest in formula? 
I plan to breastfeed my son until at least 1 but my neighbor told me that I wouldn't be able to do it because it was extremely painful for her and it would be painful for me.
I'm gonna buy a couple things of formula, but I'm not gonna start stocking up on it until after I have my son and I know if I'm breastfeeding or not.