One easy substitute for a crepe mrytle is the wax myrtle. It is a fast growing shrub that can quickly reach 12 to 18', rounded, evergreen, is brittle and ice will certainly break limbs. The old fashioned Japanese ligustrum can be trained to a small tree form, I've always found the fragrance of the May blooms to mean the start of swim season to me. If you soil is a bit on the dry side the Texas Mountain Laurel is lovely, if slow growing. If you actually need a tree you can look for the Evergreen elm, Ulmus parvifolia. Bamboo can be lovely, provided you are certain to get a clumping bamboo NOT the running type. Red tip photinia actually makes a gorgeous nearly-tree if you just leave it alone and do not shear it into a cube like everyone seems to need to do. It will have both red tips and white blooms at the same time, I've seen one that was over 20' tall and a perfect oval form. Finally, the native yaupon will eventually have a form similar to the crepe myrtle if you trim it as it grows taller. A japanese black pine is a possiblity if the overall design of the yard will allow that, could be lovely with an attractive bunching of grasses.
If there was situational shade from other buildings or other trees, and you could tolerate the falling leaves, a japanese maple can be lovely, if the sun is not too harsh and it gets water. Very pricey.
I suggest that you visit the Dallas Arboretum and look at the trees and shrubs there to see what things look like at maturity. You may find more inspiration there.