Plugged ducts occur even to moms who only breastfeed. I really don't think the one bottle a week really did it.
My sons both needed to be supplemented with formula. It made the process really simple. You can try this... Breastfeed but when your baby usually switches breast, give the baby 2 ounce bottle instead. The next time you breast feed, start with the other breast. If you are having problems with fullness in your breast, then try pumping as needed. Not emptying the breasts at each feeding will slowly decrease your milk supply and it allows your baby to get acclimated to the formula. You can slowly increase the amount they get at each feeding. You may find that after about a week, the baby only wants the bottle since it is easier to feed from a bottle than the breast.
Please note that with the formula comes a couple of changes... Bowels movements tend to be less frequent, the need to burp increases slightly, and the look/consistency of the stool will change as well.
Good luck! Remember that breastfeeding may be totes as what is best for babies but it is not always the case. In my case, I wanted nothing more than to breastfeed my first son. Unfortunately, with only my breast milk he was not thriving. He needed the extra calories to thrive. The best way of feeding a baby depends on both Mom and Baby. If breastfeeding is not best for you, then it probably is not best for your baby, either, and you have nothing to feel guilty about. Babies can feel when Mom's are uncomfortable or stressed. If you are uncomfortable with breastfeeding, then your baby may actually do better on a bottle. Do what is best for your family not what anyone pressures you to do. That's what I'm doing for my 3 month old (who is bottle fed even though I really wanted to breastfeed but refused the breast after he had to be supplemented for jaundice). Good luck.