Know of Bonnie Reese through the water-wise landscape seminars hosted by the Dallas/AgriLife folks. She does verbal consults through full designs. Can get a rough idea of costs from her company website: beautifullandscapes.net. It's at least a point of reference for independent design work even if you're outside her service area.

Many good nurseries also offer different levels of design services. Two in my area are the Garden Coach program at North Haven Gardens and the in-house design services at Rohde's. Unfortunately will likely have a wait for anyone with a good reputation, especially this time of year.

Forgot to suggest posting photos of your tougher spots on the GW Landscape Design forum. Have seen some great advice from some of the hobbyist and professionals that frequent that space. May provide some ideas and questions for your designer.