Words are used:

1.) muflihūn, root flH. This word is used in -> I.
2.) surūr, root srr This word is used in -> II.
3.) niʿmah, root nʿm, bliss  ( - )
4.) naʿīm: happiness, delight, pleasure, bliss -> III.
5.) fawz: victory, felicity, safety, salvation -> III.
6.) ridwān: grace, acceptance, favour, that wh is pleasing -> III.
7.) saʿādatu, root sʿd( - )
8.) tawfīq, root wfq   ( - )

I.

The whole of the religion of Islam is meant to enable man to lead a happy life here and in the hereafter. The whole meaning of this religion or way-of-life is to lead him / her to success or salvation. Because of its importance Allah says right at the beginning of the Holy Quran:

So its is very clear from the outset who are the happy or successful ones:

Those who follow the true guidance of God - Allah (because Allah speaks the truth - is the Truth, keeps His promise), by counting on the Divine power of the Unseen (Allah the Non-Manifest, God which we cannot see - but Who is never-the-less there), those who establish prayer (even if difficult at times), who spend from their own money in Allah's way (which includes well-defined objectives and conditions, and even if he/they would like to keep it for themselves,) who follow in their daily life the quranic revelation and the {gist of the} older revelations and who have the assurance of the Hereafter.

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As a prerequisite, those living a life 'in the dark shade of Allah', (ignoring His rights) must first understand the fault of their life and repent fully:

Because the Revelation is the truth in all ages and situations {it is either for you or against you!} and a light given to the Prophet ﷺ :

In all what one does one should do it for Allah's good pleasure, for His face, for we will one day stand before Him, answer for our deeds:

Here we see the fastest way to happiness and prosperity by gaining Allah's good pleasure (ridwān): giving to the needy, first of all those in your family. This for countering the innate tendency of the nafs (egotism), to keep the goods for oneself, or to hoard. Therefore Allah says:

Therefore it is important to strive (a) earnestly on the way, while obeying (b) the Messenger of Allah ﷺ :

→ a) → b)

By thus following the Islamic tradition, represented by Prophet Muhammad ﷺ , the believers will be enabled to do good (d) themselves [hastening to do good works(e)!] and also to enjoin good (c) and forbid evil (at the social level - not always and everywhere, but subject to specific conditions):

→ c) → d) → e)

Then those are the ones finding good pleasure in Allah (ridwān), because God is well-pleased (rdw) with them, forgiving them their mistakes:

II.

1.) The hadith show that Prophet Muhammad ﷺ was a very a kind, generous and happy man:

Narrated ʿAbdullah bin Ka'b:
I heard Ka'b bin Malik talking after his failure to join (the Ghazwa of) Tabuk. He said, "When I greeted the Messenger of Allah ﷺ whose face was glittering with happiness (surūr), for whenever the Messenger of Allah was happy (idhā surra), his face used to glitter, as if it was a piece of the moon, and we used to recognize it (i.e. his happiness) from his face."
Al-Bukhari, Book 56, Number 756

2.) The advice was to be happy in joyful contentment (surūr), while being aware of the snares of the dunya (wordly life)!

Narrated Al-Miswar bin Makhrama:
... On seeing the Ansar, the Messenger of Allah ﷺ smiled and said, "I think you have heard that Abu 'Ubaida has brought something?" They replied, "Indeed, it is so, O Messenger of Allah!" He said, "Be happy ('abshirū), and hope for what will please you (make you glad) (mā yasurrukum). By Allah, I am not afraid that you will be poor, but I fear that worldly wealth will be bestowed upon you as it was bestowed upon those who lived before you. So you will compete amongst yourselves for it, as they competed for it and it will destroy you as it did them."
Al-Bukhari, Book 59, Number 351

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III.

Some other quranic concepts are used to describe the very positive state in which the faithful Muslim will be in, inshah Allah:

naʿīm: happiness, delight, pleasure
fawz: victory, felicity, safety, salvation
ridwān: grace, acceptance, favour, that which is pleasing

The striving on the way is polishing the mirror of the heart: then it will reflect the Divine light and faces will lighten up:

This will happen in the next life, in paradise, but it will also already start to happen here, and this is a distinct difference to other religions, which await everything good after death. This striving is against the commands of the nafs (ego), which entangle us in this dunya. Instead we are summoned to {have} faith in God and his messenger ﷺ through right action (→ intention [1]):

Once he commits himself to Allah's directive, He - may His majesty be exalted - will help him to purify his actions (→ intentions [1]) {then he'll be among the Righteous and Pious (sālihūn) inshah Allah}.
{Because} the value of someone whose whole purpose is Allah's pleasure (ridwān), is Allah's pleasure on earth and in heaven:

Who would not be happy being accepted in the best way by God Himself - Allah - may His majesty be exalted. Ridwān is the greatest of Allah's doors, as the shuyūkh have said [2]:
“Whoever has been given ridwān has received the most generous welcome and is honoured by the highest nearness (qurb) {to Allah}. ʿAbd al-Wāhid b. Zayd said: 'ridwān is the greatest of Allah's doors, and the paradise of this world (dunya).'”

“and know that man cannot possibly be content, in peace or pleased (rdw) with God, before Allah is not well-pleased with him. For He - may His majesty be exalted - says:”