I always tried to pump the same amount that my kiddos were eating, so in your case my goal would be to pump 18oz/day. Maybe do another dual pump/feed in the afternoon, just to pump that extra 2-3oz? I would do a little pumping with my first feeding after work, as I usually had a pretty good supply built up by then, and I always got more pumping when the baby was feeding on the other side. With that little extra, you are not hitting up your back up on a regular basis. I usually sent my kiddos to daycare with 3 feedings plus a small bag with 1-3oz that the sitter could either feed or mix with a little water and feed if I was running late. Worked out great, but still a ton of work. I know exactly how stressful it is to try to keep up on that supply!! You are doing a great job :)