I do both. My supply has diminished since I haven’t been pumping as much, but I’ve gotten it up to “just enough” by pumping every 3-4 hours daily. I haven’t latched baby in a long time, but I give her pumped breast milk in the morning and afternoon, but I give formula closer to the evening so she is a bit more full for bedtime. It’s been working for us
You can pump your breast milk. The cluster feeding actually builds up your supply so keep her on the boob as much as you can. If not, pump during those bottle feeds. Even if she got 1oz of breast milk daily, it still meets the benefits of breast feeding. I was the unlucky one who didn't have a good supply because my son wouldn't latch; I was pumping for 3 months and combo feeding. The sole pumping was so depressing and a hassle that I just gave up pumping at the 3 month mark and he went fully on formula. There are women who solely pump for a very long time. My advice is to keep breast feeding. I can tell the difference between my son and others in terms of an immune system. My son constantly gets sick. So combo feeding is actually better than going to formula 100% but I really wish I got to experience the breastfeeding part in my mom journey and give him those benefits for longer. However, mental health matters too. So do what is best for you and your baby.
To get her used to formula, you would mix like 1 oz of formula into the breast milk every few days to see if she can tolerate it. Watch her for any allergies or constipation. Then increase the oz to 2 of formula and the rest breast milk until you are at 100% formula (if you wanted to do a 100% bottle of formula). You can do 50-50 of breast milk or formula once you know she tolerates the formula and gets used to the taste. There are formulas for sensitive tummies or lactose intolerant, allergies, etc. so ask your pediatrician what they recommend to start.
I breastfed and pumped through the first 4 months. That’s when I got my period back and saw a significant drop in my supply. The pediatrician said it would be helpful to me (less pressure on me) to supplement with formula. I started adding one ounce to two ounces of breastmilk (we buy Bobbie Organic formula.) The ratio shifted around a bit (sometimes half and half) but now (7 months old) I’m back to breastfeeding (he eats purées++ now too) and pretty much only breastmilk unless I’m leaving baby with Dad all day and with not enough milk (I work part time/ once a week). It turned out that the saying I heard from lactation consultants, “your body will produce the amount of breastmilk your baby needs throughout the changes he’s going through” proved pretty accurate. My tip: I’ve been a fan of the manual pump and Tommee Tippee bottles (nipple size 0). Pump or nurse every 2 to 4 hours. You can always freeze the extra supply which is great to have later when period comes and supply slows.