Rue - we lost 12% of birth weight and it was 3 or 4 weeks til he was back to birth weight. However, since then he has gained in leaps and bounds and is leaping back up the centiles. I had the top up pressure in hosp particularly re jaundice.
He had 2 or 3 formula top ups BY CUP then we were topping up with ebm, again by cup until he stopped losing and started gaining. We were doing that when discharged at 6 days.
Thankfully, community midwife was far more realistic. Diabetic mother, baby brought out early and section were all going to make it likely he'd lose at first. 'No wonder' she said and encouraged me to drop the top ups as they were running me ragged (by the time I'd fed a sleepy baby every two hours, expressed and cup fed I had half an hour off then had to start again!). After that it seemed so much easier.
My suggestion would be to feed every two hours if you can, waking him if nec and keeping him awake by stripping, changing, feet tickling etc. you might be able to avoid top ups.
If you can't avoid it, ask mw for some of the special cups to use to give him ebm.
Btw, am sure we were still on green pops by a week. She sounds a bit hysterical to me!!