switching to breastmilk AND formula

Don't think I can tolerate breastfeeding any more - Iv tried nipple sheilds and lactation consultants but 7 weeks later it's still excruciating and I'm so exhausted 
I feel guilty because I have a good enough supply but I'm not sure I can commit to exclusively pumping (but I feel selfish for this)
I'm thinking to do 50/50 formula and breastmilk so I don't have to constantly me pumping my boobs but stil can provide my baby with some breastmilk 
What do you think? Is a god idea? 
Should I mix my milk with formula? Or should I do one feed formula, one feed breastmilk?
Any advice or tips? Should I try pumping exclusively??