Originally Posted by gardengal

Here, they sell such things as "patio trees" - these are typically
hardy, often flowering shrubs that are trained as or grafted to a
standard or 'tree-form'. Lilacs, physocarpus (ninebark), hydrangeas,
flowering currants are examples and there are numerous others. Dwarf
flowering crabapples are often used in this manner as well. If it were
not a full sun location and with the potential for reflected heat from
the patio doors as well, a dwarf Japanese maple would work as well.

Wanting to reach your height specifications plus be hardy enough to
remain outdoors in winter (will this be planted in a container or in
the ground?) pretty much limits your choices to small trees or
shrubs. You need to look at something hardy to at least USDA zone 7,
ideally a zone or two lower.