Portable couches are the obvious first choice for practicality and the basic models are a fixed height. You can specify the height you want, but cannot adjust it after that. It will always be a compromise as patients come in all sizes. To be able to apply deep massage techniques using a good working posture the couch needs to be fairly low. A general guide would be level with the tip of the index finger when the arm and hand are hanging down by your side.
Therapists using lighter and gentler techniques usually prefer a higher couch.
There are adjustable height portable couches but they have to be set before the patient gets on. These are ideal if several therapists are going to work with the one couch. They are more expensive and usually heavier than the fixed height couch. The standard width of a couch is 24 inches. Although a wider couch may be more comfortable for the larger patient this may not be ideal for the therapist.