Sounds like this sort of thinking could deter you from endeavoring to do good and participate in virtuous deeds, so you'd basically be a human, come across the dharma, and leave "this island of treasures" empty-handed because of wrong view.
In the ultimate view there is great equanimity. Our karma is constructed from action and intention. We will reap the results of all the karma we create, later or sooner, and in proportion kind and exponential to how we have treated others.
This is a huge obstacle in this era of degeneration because people live in their conceptual mind. They are not rooted in their bodies or in their senses as much as in they are dancing in their concepts and thoughts. Body scans work as a strong antidote for anti-doting.
If one was truly separate from the world, seeking liberation from pain and suffering might be selfish because it might be possible to be an independent, enduring, unchanging "self" that extricates (itself) from suffering and pain. But, as we are interconnected and interdependent with the world and one another, the only thing that resembles a "self" is actually our attachment and our mis-identification with the skandhas as a self.
So, when we increase our karuna (compassion) and weep for all the suffering beings of the world and all the realms, we tap in to our natural abode which is a selfless abiding of awareness. It's not possible to get to it without compassion. Basically, we are obsessed with being a leaf on a tree, and when we remember all the other leaves we start to furnish our embodiment back into a whole tree, not just the leaves and branches. In this analogy, other beings are the other leaves and branches.
Shantideva said "we are all petals on the lotus of life"
Think like this.
Remember that for something to truly exist it needs to be independent, enduring, unchanging. Can we point to anything that is truly independent of its context, environs, surroundings, interactions and so forth?
Wishing for freedom from suffering or pain is not selfish, it is intelligent. There cannot be selfishness for a magnanimous mind that has empathy for all. It is simply "the best path forward." Until one has compassion that encompasses all sentient beings, one will be operating on a smaller level with smaller ambitions, but even then one will inadvertently help other beings through their own minimization of kleshas and adverse negative emotions and so forth.
I think this sort of question is very self-righteous and arrogant, for it assumes: there is a self, the self does whatever it can to feel good, and therefore anything that is done for the self to feel good is "selfish." This is based on a faulty premise, so naturally the result is faulty.
Yes, there are three vehicles in Buddha's teaching. It takes great understanding and great compassion to foster and engender the mighty and noble mind that wishes to liberate all sentient beings. This comes through study and reflection, and understanding that all beings are just like ourselves, wishing to be free of pain and suffering and wishing to have happiness and bliss and freedom. In this way we are all very congruent, very near in modus operandi.
At any rate, it is not selfish to want to free oneself from pain, because this is endemic to all sentient life. It is more selfish to think that the extreme of nihilism or eternalism is valid and to act according to those ideas as if there was no such thing as continuity. That would be "selfish" because it would truly be unhelpful. One must be helpful.
In teaching that way, it's clear why one ought to practice and engage in right action and right livelihood. You gotta get people interested somehow, gotta get the foot in the door so-to-speak. Then, when people see the benefits, they grow full of ease and comfort and joy. But they are also confronted with many other beings in their daily lives, who are not happy, who are discontented, who are in pain and suffering from afflictions both self-inflicted and not. Then, compassion and empathy grow. Then, the bodhisattva ideal takes root. One is not doing it just for oneself, but one knows that there are beneficial results to practice -- the best possible results for our Experiential Reality (that is interdependent with all Life) come about only through practice and when there is an opening one can access the depth of honesty, the depth of real experiencing.
So in my opinion, it is mainly a matter of mis-identification.
Mis-identification with the skandas as a self that is permanent and unchanging and independent from the rest of the cosmos/matrix.
And mis-identification with an idea as somehow superior to the infallibility of cause and conditions and effect.
If I give someone water to drink because I think I will be rewarded in the future -- firstly, that's true, secondly that's skillful means on the part of the teacher. I help someone, they are truly helped, suffering in the universe is diminished, everyone wins. Plus, it is good for the giver. "The giver always goes to a better place." It is true, it is flawless knowledge, it is genuine and real Dharma.
But then one says "Oh pish posh you are only doing that to benefit yourself in the future."
Well, think about it. Who is going to benefit? If I am broken down and unable to help others, I must receive help or endure the suffering. If I am in a good position, I can help more people. I have been clinging to a material reality and the skandhas for so many go-arounds that I perceive my skandhas to be independent, enduring, unchanging, and fail to see how there could not possibly be an actual "self" in them. That said, I must liberate myself before I can liberate others, and what we have come across here is a stepping-stone to the heart of great empathy and great karuna and great love. Yes, do so out of a wish to help yourself at first, and then see the equality of self and other. See the equalness in wishing to be free of pain and discomfort in the smallest fly and the largest whale. It is not something that requires magical thinking, it is from our true, lived experience.
So yeah, don't conflate pop psychology with skillful methods of a realized presence. The first wil lead to hardened and intractable notions of a "self" versus the "world," the latter will lead to freedom for self and other - which, when discerned with wisdom, are found to be equality.
When you give, you'll feel better, and your ride will ultimately be much smoother.
At first, this can seem like a call to help oneself.
But really, it is a call to help those around you while recognizing that there is a benefit not just for one, but for two, for all.
We must crawl before we walk, and walk before we fly.
Do not make jest of that which frees beings from bondage suddenly or gradually.