An LSE survey of 200,000 people showed that the two things which most made people happy were good mental health and having a partner.
A doubling of income had only 1/3 the effect of gaining a partner.
This does tie in with other research I have seen which said that once you hit a threshold, having more money doesn't make you happier.
On a scale of one to 10, the doubling of someone's pay saw their happiness rise by less than 0.2. The researchers said this was down to people caring more about how their incomes compared to other people's than how it affected them.