Hello, Dreamer08. Congratulations! A new baby is very exciting.
Let me remind you that it is your decision to breastfeed your baby, not your mother-in-law's. The only reason why you might need her support is if she is babysitting and feeding expressed milk, but obviously you have control over your baby and your own body, particularly in these early weeks.
I suggest you tell your grandmother that you want to do the very best for your baby / her grandchild - and breastfeeding is widely acknowledged as the best source of nutrients for a baby. Focus on looking after "her grandchild" but don't lose ownership of your role as "mother".
If she is telling you that she bottle fed your husband and he turned out okay, agree with her ... but make clear that was her decision. Now it is your turn to make your decision. Tell her how you will breastfeed your baby for as long as you can, and you would really appreciate her support because when the child grows up, you want to be able to tell stories about how helpful their grandmother was.
Gently remind your mother-in-law of her role and say, "Nobody wants their baby to be in a family where there is conflict. Please, it is my turn to be the mother now, so please support me."
The time might come when you choose to bottle feed, but I think you've made a wise decision to breastfeed.
Good luck, Dreamer08. :)