Switch back to the breast milk if you can. Formula is not nearly as easily digested, and a cold turkey switch can cause lots of discomfort, constipation or diarrhea. If you want to switch to formula permanently, you should taper the introduction of the formula over a week or two...gradually decreasing the amount of BM, and increasing the amount of formula. Our daughter had a protein allergy, but the reaction to the formula was worse then the reaction to the BM.
If you want something to help with the reflux/spitting, talk to your pediatrician. Ours allowed us to thicken breast milk with baby rice cereal. It's a very small amount of cereal but it makes the milk "heavier" so it's harder to reflux.
Does he scream when he's spitting, or is he a happy spitter? If he's screaming then there are medications that can be considered that make a HUGE difference, and you can continue breastfeeding and supplying the immunities that they so need during cold and flu season. If he's a "happy spitter", I'd go back to the BM and just watch his weight gain. Often times they outgrow the happy spitting around 8 weeks old...some later.