Are you processing from RAW or from .JPGs?
RAW will allow more latitude to tame the blown-looking whites using controls such as Highlights, Whites, contrast, Curves, stretching the histogram, and of course Exposure. While shooting try to keep EV at no more than +1/3 or keep it flat at 0, and then work on the other tones, including whites and increase the white levels to near 255 in post (if desired) if they were too low from an EV of 0.
I shoot IR with a polarizer to achieve darker skies, which also tends to increase the contrast and will push some whites to 255, so I am almost always trying to pull down the blown-out whites in post.
I do leave some grey in leaves and clouds since they shouldn't all be pure white, just like in any other B&W photo.