Breastmilk and Formula

I have been pumping less and don't make enough each day for baby. Should I use my freezer statch to fill the gap each day or use formula to supplement?

If I use freezer stuff, he will be on solely breastmilk until 9 months but then he will have to be in straight formula after that.

If I mix formula in now, he will have a mix of both breastmilk and Formula until age one.

What would you do? Thanks!