I have a question about introducing formula and potentially weaning my baby, would love some advice.

So my little girl is four months old, and at her most recent doctors appt her doctor asked me to start giving her formula. She's healthy but she's fairly thin, so we're basically trying to plump her up and get her in a better weight percentile (right now she's in the 4th percentile).

So my main problem right now is that I want my breasts to keep producing milk, but I'd like to switch over to mostly formula. Is it possible to do mostly formula but still breastfeed when I need it? More specifically, I want to breastfeed at bedtime and nap times. I've been giving her one bottle (always 2oz) at night and one in the morning, and I'm very interested in making the switch to formula for the sake of baby's health, but I still want to keep the breastfeeding line open for bedtime comfort feeds and nap time comfort feeds.