Hi! This is a great topic:) Here is a few suggestions from a first time reader  
  
... factors with regard to achieving happiness - Since you already mentioned happiness previously, this feels like an unnecessary add on that makes the sentence look busy and a bit meaningless, I recommend rewriting in to highlight your point.  
  
"Happiness is quite ... it is quite abstract" -two "quites" in a sentence  
  
" For example, some people ~~who~~ feel happy ... they have loving familes, or have free time totalk to their families, friends" - I would divide this into 2 sentences. reiterate the fact that for some, physical needs like shelter and substance is already the peak of happiness because they do not have anything greater (if that's what you mean). And for others, a sense of belonging with their family of communication is what makes them happy; because they do not need to worry about finding for a shelter for the night, they are trying to fulfil their psychological needs.  
  
*side note: check out the maslows hierarchy of needs, if this is a research type of paragraph, the model will tell you a lot about how happiness is perceived by people of different life situations.*  
  
"This is because, ... Thanks to this, ... Others factors could ..." - read it over again, and rewrite a bit.  
  
It looks like you only really mentioned one or 2 factors.  
-everyone perceives happiness differently  
-you can't define happiness.  
I know this probably has a a word count but I would explore deeper the issue because right now it seems as if you are repeating our point every sentence and it doesn't have a structure.  
  
maybe begin with describing why it is different for everyone, like since everyone is at a different stage in the hierarchy for example and there are physical and psychological needs that have be met and therefor you will never reach the "happiness" you seek without the other.  
  
then you can go into why people strive to be happy and why it is so difficult to pin point what it is exactly even for yourself. do you think you are happy? what does it mean for you? do you think some people are not happy because they have a wrong sense of what happiness is supposed to look like and they will never reach that point in life because they truly do not understand if that is the happiness they want? --- sorry I feel like this is off topic  
  
So yes, everyone is different. they all have a goal and a final destination of "happy" town. but everyones map to the town is different. Happiness right now is viewed from a collective perspective. You know you log into your insta account and you see people on private islands with families that love them and they are financially stable. So everybody who likes that photo of them collectively think, "yesss, this is happiness, I am not going to happy until I reach that". But that's kind of wrong dont you think? Happiness should be an individual subject. --- I think this is a good point to include as well. A single state of happiness can't be universal. It is very personal and that is why it is so hard to define because there are 7 billion of us ... 7 billion types of happiness that we haven't even discovered yet ourselves  
  
Sorry for rumbling on, just wanted to give you some ideas:)