About the tomatoes. If you cannot find really fresh ripe tomatoes, use tomato juice.
About the yogurt. Do not use vanilla or flavored yogurt.
Optional. Katzen's recipe included "several" fresh raw mushrooms thinly sliced. They don't work for me. What does work for me is 6 grilled shrimp or scallops. She garnishes with watercress. I like the basil better. You might want to garnish with chunks of avocado and sprinkle a crumbly cheese like feta on top.