I went back to work with similar hours when my son was 10 months old. I did end up giving the babysitter sippy cups with cows' milk or watered down juice because I hated pumping and it didn't seem worth it. I nursed him in the morning, dropped him off at the babysitter's, then he'd eat some solids mid-morning, sip a few sips of cow's milk if he was thirsty (and he usually didn't touch it), then I'd come at lunch, nurse him, and then he'd nap. When he woke up, he'd usually drink about an ounce of sippy cup milk and possibly have some solids. I'd come pick him up after work and he'd nurse at that point. We'd still have hours of evening cluster-feeding and another bedtime snack of solids before he went to sleep for the night, and he still woke up several times in the night to nurse.
Like you, we didn't even do this every day, just 2-3 days a week. Honestly, I don't think you need to worry much about disrupting breastfeeding, although it totally stressed me out for the first few weeks, too! My son still nurses like crazy at 14 months.
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