Formula while breastfeeding

Sarah
I hated every minute of breastfeeding my first baby. We went 14 months because I felt like a bad mom if I stopped (Not that those who go with formula are bad moms; just that I was able to breastfeed perfectly fine and I didn't want to and I felt bullied by the breast is best campaign to continue.) 
I know it's possible to do both and I think I'd be able to soldier through breastfeeding my next one if I knew how to do both. 
What are your experiences and tips? How did you do it?