Breastmilk to formula

My lo is 6 1/2 months old and breastfed but my milk is getting lower and he isn't taking the boob well and I am just done with it all. I know breast is supposed to be best but I'm sticking to fed is best. The problem is he will take formula in a bottle mixed with breastmilk instead of water. But he won't take formula mixed with water! He would starve himself instead! Anyone ever experience this? How do I get him to accept it? Right now I'm pumping like crazy but he eats more than I pump and my freezer stash is almost nothing now :;"(