What about having baby assessed by an IBCLC to find out why baby is not transfering more milk-assuming milk transfer is the problem?
Supplementing with anything while sometimes needed and helpful, does not solve the underlying problem, which appears to be that baby is not getting enough milk at the breast. If a baby is not getting enough milk at the breast, it is due to 1-not nursing often enough, 2-baby not nursing well enough (not able to get enough milk out per session) or low milk production-the milk is just not there, or not enough. or a combination of these.
A good, experienced IBCLC could spend an hour or more with you and assess the situation. She cannot overide a doctors order, but certainly she should be able to help you figure out what is what here.
If you have to supplement, of course it is better to do so with your own milk when possible. What type of pump are you using? pump type/age etc, often makes a difference in what a mother can pump.
I don't know if you need to supplement or not, but again, there are ways to do it that are usually less impactful on breastfeeding going forward.
I suggest you call your local LLL if possible. They may know what breastfeeding support options are available. You can also look up IBCLCs here http://www.ilca.org/i4a/pages/index.cfm?pageid=3432