You are definitely not a failure.
I was never able to pump enough so I started supplementing pretty early.
One problem you might encounter since your ds is so much older is that he may not actually drink formula. I never tried it, but I hear it doesn't taste so good and sometimes if you wait until they are older and they are used to the taste of bm they will just refuse to drink it. If that's the case you might need to look into alternatives to formula. I read some interesting info about goat's milk, that it was a good alternative to breast milk, though I'm not sure about the allergy factor.
Also, I agree with other pps that maybe by increasing his solids (especially calcium and healthy fat rich foods) while he's at day care as well as feeding him last thing before you drop him off, and first thing when you pick him up, you might be able to eliminate that second bottle long enough for him to be old enough to not need the formula at all.
As for introducing cow's milk, we did it pretty slowly and she refused to drink it for a while. She still won't really drink it when I'm around, but she drinks it at day care.
“We are not put on earth for ourselves, but are placed here for each other. If you are there always for others, then in time of need, someone will be there for you.”