What are the trees called that have cotton ball looking blossoms?

Bradford pear,dogwood

Sounds like it could be a Bradford. Something like this?

Bradford pears have fallen out of favor because of their tendency to split at branch crotch. My entire neighborhood was planted with them years ago, now they are all gone due to splitting...sometimes half the tree would break off in a storm. Try a disease resistant dogwood, or a magnolia, maybe? Star magnolia is pretty. Look online for ideas.

Tulip bush, a hybrid magnolia has magnificent huge tulip flowers for thirty days and then it leafs out to look like any other magnolia but it looses its leaves in the fall. Mine was about 15 feet in diameter and 15 to 20 feet tall. People always stopped their cars for photos when it was in bloom. Mine had red flowers.

I think its a mimosa tree

My mom had a large shrub/small tree called a snowball tree. I suspect that's what you mean.

I think the common name is a snowball bush