All Salix varieties are ok in damp conditions but Salix 'Hakiva Nishiki' I reckon would fit the bill, has a lovely pink flush of leaves in spring turning lovely creamy white, I have had one now for 15 years and is approx 6ft, Also Sorbis Aucuparia would be ok but grows a bit taller, but it easy to keep under control

Try Nyssa sylvatica, a bit rare, and fantastic autumn colour. I'm on clay, and it has done well for me, but I 'd be wary of chalky sites. Phil J

Magnolia virginiana 'Plena', maybe?

Plenty of food for thought thanks.