For that matter, the same argument could be used to say "Out of humility, I'm not going to try to save my soul, because I don't deserve heaven." or "living a life of virtue is more predictable and pleasant, so I will forego that to mortify my self-love".
Doing God's will and mortifying your passions WILL lead to more happiness on earth -- at least the most important kind of happiness, which includes peace of soul. Moreover, you also have a chance at happiness hereafter.
God did implant in each of us the desire for happiness. That is to be found primarily in heaven. But, as St. Teresa of Avila said, "Heaven is on the way there."
On the other hand, those who lead a life of sin and vice often have horrible sufferings here (unquiet conscience, guilt, envy, regret, unfulfilled lust, etc.) AND they end up in Hell. You could say, "Hell is on the way there" as well.
So it's not self-love to follow God's plan for us -- even if that makes life better for us here AND hereafter. It's more like a win-win situation. It's what a wise person would do.
Matthew