This is a good question and has a myriad of potential answers. Fundamentally, if you are in a state of happiness you do already have everything you "need" - or you wouldn't be happy.This would however be an incomplete answer because it would suggest that desperately poor people are never happy - which is not true. They find happiness in the smallest of things. The unfortunate thing is that this sort of happiness cannot be sustained.
Having everything you want could be a double-edged sword as the more you have the more you want and a cycle develops. There will always be something else you want next. This infers that a person can therefore never be happy.
Life and behavior is extremely complex and a simple question about happiness could become very involved in its answer.
This question has one more important component and that is the word "decent " human life. This is a very relative question as the things that have the potential to make one person eternally happy are not the same things that will make another happy.
In other words, it seems that material things then are not the basis of happiness. They create short-term happiness or even the illusion of happiness which is soon shattered by reality.
Happiness is an emotion and, as such, changes constantly. A person's concept of "decent" infers that there is a moral aspect to living happily ever after. Therefore there are responsibilities that go with being happy that must be fulfilled in order to find contentment. Consequences must also be considered.
Happiness is a state of mind and, as such, each person has his or her own concept of it. The most apt answer then would probably be that neither what you want nor what you need brings you happiness but what you do with what you have and HOW you live your life will bring you happiness, on a long term, ongoing basis.