Supplementing breastfeeding with formula??

🚨Long post but I need advice moms 🚨

So my baby is exclusively breastfed and ever since his acid reflux diagnosis he is on zantac, sometimes we use gripe water/gas drops & I have stopped consuming dairy as a precaution, which was suggested by the GI specialist just in case. However, he is still very gassy and spits up quite a bit (even after feeding him in an upright position, burping him for 20mins after, etc... 🤦🏽‍♀️) He is gaining weight & digestive system is healthy otherwise. His gassiness seems to increase anytime he is on his back (incline or flat) so during naps & at night he is constantly grunting and in pain 😞 I have been told with time his digestive system will mature & it gets better (makes sense, I know) but I have also started thinking of possibly supplementing with a formula that may help HIM feel better *my top priority*... In a perfect world I'd want to only breastfeed & he wouldn't have these issues but yeah... Any suggestions or personal experiences on supplementing with formula while still breastfeeding? & I'm not too fond of mixing cereal with my breast milk. More along the lines of replacing a feeding with formula. I still want to primarily breastfeed. Please & thanks!