I mulch everything that is the first layer of defense and usually good enough. I also have some plants that I move to areas where they will get less sun in the summer months if they can't handle the heat. Another option is building a sun shade with a bit of screen directly over your plants to reduce the mid day sun.

I've had a raised bed in the DFW area for 6 years. My vegetable plants never do well in the heat of the summer. When the weather begins to cool a bit, I've gotten good production on my Roma tomato plants. A greenhouse would only work for you if you wanted to spend the money cooling it. My greenhouse gets to 109 degrees inside, in January if I don't open it up. That's with shade cloth on it.