Thickening w/oatmeal for reflux- Nipple ?

monkey62

Per our GI Dr., we are thickening DD's formula with oatmeal ( 1/4 tsp. per oz.) for reflux. We use Born Free Bottles and cannot find a nipple that works. Level 1 and 2 are too slow and are getting 'clogged'. Level 3 and Y cut are way too fast. I tried using a knife to open the 2 a little more and it didn't work.  Should I switch bottles/nipples? If so, to what? Should I switch oatmeals? We use HappyBaby Organic.

Thanks!