I don't recommend reptisoil because it contains peat moss which is environmentally damaging/not sustainable.
I like mixing cypress mulch or fir bark with the coco fiber. Those hold moisture well too, but don't get super dusty as they dry out. I've also been looking into trying coco chips over fiber.
As far as consuming their substrate . . . I look at it as snakes don't get tong fed clean animals in the wild. They eat dirty critters that have been digging in the dirt, have twigs stuck to them, etc. If reptiles have survived millions of years more than likely swallowing dirt just about every time they eat, our snakes are probably okay if they swallow a little substrate by accident. Plus, animal fur passes through them just fine.