Adding formula top ups

My baby girl is 4 weeks old and still isn’t back to birth weight. I’ve been working with my public health nurse and LC and have been triple feeding for 2 weeks. Luckily she’s gaining weight and is happy, alert and meeting other milestones, but we now have to up her top ups and I just don’t pump enough to meet demand.

I have very little experience using formula. We’ll be starting off small and going by baby’s hunger cues, but has anyone done combo feeding for a short time and transitioned back to exclusively breastfeeding?