I've run the gambit to be able to breastfeed. I've done suppliamental feeding systems to avoid nipple confusion when suppliamenting was necessary, I've taken fenugreek, blessed thistle and domperidone to increase my insufficient supply, I've pumped after every feeding for days in a row even when they were only 1.5 hrs apart to begin with.........and I know the guilt you speak of when contemplating whether going with formula is just easier.
Even I don't think I'd try in your situation. At some point you just have to accept that it's more important that you feed the baby rather than what you feed the baby. My first two grew strong and heathy on formula after the first early weeks of trying to nurse.......yours will too.
Good luck with whatever you decide.
Shannon