First and foremost, you are going to get a lot of flack from women about using formula at all. Just ignore them, they do not understand the difficulty for some women or obstacles that do not allow all women to breastfeed.
Now that I got that off my chest, here are a couple of options for you.
First, try feeding less, more often. Sometimes this will help with the spit up issues. I am nursing my 4th baby and she pukes constantly, so just remember that not all puky babies are because they are on formula.
Next try putting a small amount of corn syrup in the bottle with the formula, about 1/2 tsp. for every 4 to 8 ozs. This will help with the constipation. The rice cereal will help with the puking but will make him constipated, the corn syrup will help here.
Next, really establish if he is uncomfortable with the spit up or is he just puking without much fuss. If he is not uncomfortable I wouldn't keep changing formulas, this could make him more fussy. I know for a fact that the constipation will really upset his tummy so maybe focus on that. If he is really uncomfortable with the spitting up, then try Baby Bliss Gripe Water. You have to use the Gripe Water by Baby Bliss, other brands carry Gripe Water and it does not work. This will help with an upset tummy. Just give a tiny bit before and after eating or any time it seems he is uncomfortable. It is 100% natural herbs and perfectly fine for babies.
If at all possible I would stay away from the drugs. I think we are WAY over-prescribing in America these days and our bodies are made to fix itself on a lot of fronts. I will admit that with my second child I used a prescription drug for what they call silent reflux, but he was in SERIOUS pain all the time. After about 2 moths of the drugs working successfully I discovered the Baby Bliss Gripe Water and was able to take him off the scripts (he was also breastfed).
I hope some of these solutions work for you, I would try them before switching to Nutramigen. That stuff is seriously yucky tasting and hard to get babies to eat it.
Good luck!
P.S. I didn't make it clear that if he does not have an upset tummy with the puking then let it be. Babies puke and it is fine, maybe a pain for you but fine for them.