Crack willow (Salix fragilis) is a natural waterside tree but it's twigs are very brittle. the leaves are a greenish-gold colour.
The silvery leaf that you mention is possibly that of another native, the white willow (Salix alba). Both will take up a lot of space and may need a lot of pruning to keep them within reasonable, manageable size. I would not recommend planting these trees, as beautiful as they are, close to buildings, as the roots can be invasive to drainage and foundations.
An alternative to willows may be flowering 'Dogwood' (cornus)