A portrait is typically defined as a likeness of a person, especially of the persons face. In the film world "portrait" lenses were generally 85mm to about 105mm and have a wide aperture: f/1.4 to f/2.8. You typically don't want to get to close to the subject. You'd want to have some space between the camera and subject to at least allow some comfort space and a feeling of not being crowded among other reasons. When translated to the digital world a "portrait" lens would be about a 50mm to 85mm, again with the same wide apertures.
For full body shots the photographer would just move him/herself further back from the subject or move the subject further away. This is something that you can't do according to your OP. The next logical step is to look for a wider lens and you have found just that, and a good one too. It will definately suit your needs. Its up to you to decide if its worth the $1000.
Another lens to consider is the Tamron 17-50mm f/2.8 Di II LD Aspherical lens. Its less than 1/2 the cost and seems to be getting some excellent reviews, at least over at
amazon. I haven't checked other places, but it might be worth looking into.