I would propose that you are happiest when you have enough. In this graph, which was very similarly presented in Your Money or Your Life by Joel Dominguez and Vicki Robin, the essence of happiness with stuff is communicated beautifully.
As you start to acquire things, your happiness starts increasing. Up, up, up goes your happiness. As you acquire more and more, you reach levels of joy previously unknown. But, then something happens.
At a point, you reach the highest your happiness will ever go. After that, the more you acquire, your happiness goes down. If this weren't the case, wouldn't hoarders be in a permanent state of ecstasy? This truth is why we have so many people with so much who are miserable. Happiness can't be bought with excess.
So, the trick is to find "enough." Find your level of satisfaction and contentment. Pray for it. Want what you have, and you will have what you want. Your little will be a lot, and you will have the maximum amount of happiness from your stuff that you can possibly have.
Contentment is great gain. Find your enough.