All you need to look for with cold rice cereal is 100% rice on the ingredient list, sometimes called puffed rice. No sugar, nothing else. I’ve used several brands. Most are sold in bags, not boxes, at health food stores, and I’ve seen it once or twice at regular grocery stores. You can order in bulk from Amazon too.
Rice Chex contains sugar, sometimes in multiple forms. Avoid.
The hot rice cereal you mentioned is fine if you do okay with brown rice. White is actually better for some people, digestion wise. Either is good. Also, there’s a product called Rice 'N Shine. It’s rice grits. Also a good choice.