If you want to have really fluffy clouds in your photos, you basically have three options: The most time consuming option is probably shooting on a day where the weather fits. Your second option would be to compose some clouds in (there is quite a wide selection here). But the most fun way would be to create your own clouds.
We shared one method before which involved balloons and pillow stuffing, but this method was is definitely more fun, and kids friendly. Not to mention it will make your house smell nice for about a week.