Start supplementing??😔

My baby boy is 8 months old and he was exclusively breast fed for 4 months and since then we’ve been pumping. We’ve blown through almost all of my stash and idk if/when I should start supplementing formula. My supply kept s dwindling down no matter what o do..I’ve tried literally everything. I have about 2-3 days worth of frozen milk plus I’m pumping about 20-22 ounces a day. Should I start mixing bm and formula so he can get use to it or just wait until my freezer supply is gone? I will continue to pump until I make nothing at all. I’m so upset but idk what to do at this point. 8 months strong and I feel like my body is just telling me it’s done😔Advice??