Angela, what kind of tree was Sam? Is there a reason why you can't plant another of the same? If it was a tree that was doing well but got offed by a gardening error, it might be the best choice.
That aside, most trees are going to be tough to hold at under 8 feet (although having it potted rather than in the ground will help in that regard), and at that height, getting that much spread from one individual plant might be a challenge. You might consider a limbed up hawthorn (rhaphiolepis indica, pale pink flowers in spring are a plus), or a trio of privets, but my best thought might be a strawberry tree (arbutus unedo compacta). Let us know what you decide.

Kay

Here is a link that might be useful: arbutus unedo compacta

Have you considered an Acer palmatum (Japanese Maple)?

Check out the link I've provided

Here is a link that might be useful: Yamashitas Maples

I think you should drive around your neighborhood and find a healthy shrub in someone else's yard, take a picture of it, and then try to find a similar one. If you have a botanical garden in your neighborhood, you can go there also - there is a nice one in Berkeley. If you find something in your neighborhood, you will know that it is probably suited for your soil and climate, although my own back yard seems to have particularly bad patches of soil that need ammending.

Lars

Here in my zone I would plant a brugmansia for that purpose.

Does it have to be in a container? Some shrubby/small trees that can be kept at about 8 to 10 feet tall and are dense enough to give some privacy might include Leptospermum scoparium Ruby Glow, Melaleuca incana, Metrosideros collina Springfire, Leucadendron Safari Sunset, Cantua buxifolia, Hakea suaveolens, Chamaerops humilis.