Supplementing with Formula

R

My supply has been steadily declining over the last month or so and my frozen stash won’t last long. I need to pump 15 oz for daycare each day and it is a STRUGGLE.

What is the best way to supplement with formula? Replace one whole bottle with formula and pump to try to maintain? Give smaller bottles of breast milk and then a few ounces of formula? Mix in 2 ounces of formula with the breast milk?