Work & pumping

I am headed back to work on Monday and my baby is 12 weeks old. I work 9 hour days so baby will be in care for 9.5 hours a day. How many bottles and how many ounces/bottle should I send? I’m planning 4-4oz bottles. How many times should I pump? I know the recommendation is when baby eats, but 4 times a day seems a bit excessive.

We have been supplementing with a bottle of expressed milk twice a day since she was 3 weeks old because she wasn’t gaining weight fast enough. We give her between 4 and 5 ounces in the morning and evening bottles right now. We still try to get 8 feeds in in a day and are usually sleeping through the night.