Two great possibilities! First would be Kessler Park in Oak Cliff. It is one of the most beautiful places in Dallas. Second choice would be the White Rock Lake area. This would include Lakewood, Forest Hills, and Lake Highlands. Either of these choices provide plenty of housing choices in the price & size range that you're looking for. These are established neighborhoods with towering trees & mature landscaping.
Kessler Park, in Oak Cliff, actually has hills! We don't have many of those in the Dallas area, but Kessler Park has plenty. Kessler Park has began to emerge as one of the ideal places to live.
White Rock Lake is a definite jewel in Dallas' crown. Activities abound at the lake & park areas. You can run, walk, skate, ride, picnic, walk the dog, sail, fish, canoe, kayak, people-watch, feed the ducks, or just take a nap. Weekends, you can even chat with the "free advice guys" and get your life in order.
All of these areas offer housing that would fit your needs. Please feel free to contact me with any questions that might come up.