Simple examples:
* Her smile was like sunshine breaking through the clouds.
* His laughter was as contagious as a yawn.
* The feeling of accomplishment after finishing the project was like a warm bath.
More creative examples:
* The news of her promotion spread through the office like wildfire, igniting a blaze of happiness in everyone.
* His heart felt as light as a feather, floating on a cloud of pure joy.
* The reunion with his long-lost brother was like a symphony of emotions, a crescendo of pure happiness.
Using "as happy as..."
* He was as happy as a clam at high tide.
* She was as happy as a lark, singing with joy.
* The children were as happy as pigs in mud, splashing around in the puddles.
Using "like a..."
* His happiness was like a warm summer breeze, gentle and calming.
* The joy of the moment felt like a burst of fireworks, illuminating the night sky.
* The feeling of contentment was like a soothing balm, healing old wounds.
Remember, the key to a good simile is to choose a comparison that vividly illustrates the feeling of happiness. Don't be afraid to get creative and come up with your own unique comparisons!