Yet I still hold on to some of my old modern ways/bad companions/occasions of sin to lead me back into a mortal sin which starts the cycle all over again.

If you have a good priest who you trust, you should make an appointment with him for a confession so that he can have the necessary time to give you thorough advice.  If you are not concerned with him knowing these things outside of confession, however, perhaps speak with him outside of the sacramental seal if you think that would be more helpful.  That being said, do not be afraid to approach a priest with these problems since his entire purpose is to be a cure for souls, and, if you go to him regularly for the sacraments, specifically yours.

That being said, a few general principles :  First, avoid all proximate occasions of sin.  To willingly subject yourself to a proximate occasion of sin -- that is, an occasion in which you are very much unsure of whether or not you will be able to avoid sin -- is a mortal sin in itself.  Proximate occasions of sin are different for different people.  If the computer or TV are often the things that lead you into sin and it is not morally safe for you to use either of these things privately, you have no business using them.  There is nothing that can be gained from either of them that is anywhere near the worth of your eternal soul.  If it is necessary, say for work, to use the computer, however, perhaps ask a discreet friend who you can trust to put a block on your computer and not tell you the password.  As for TV, it should be avoided anyway, since it is essentially dumping spiritual sewage into your home.  If neither of these things are a problem for you -- if you have already thrown out your TV and do not struggle with the things of the internet, -- the same principles apply to bad companions.  If a companion is one who you are confident will have a bad effect on you but you are not confident you can affect positively, this companion is dragging you into Hell and needs to be cut off.  No friendship is more valuable than your friendship with Our Lord.  And if this companion regularly leads you into sin and you know that, if you spend time with him, he will do it again, then it is a mortal sin to unnecessarily be in his company under the circuмstances in which he could lead you into sin -- say, drunkenness, binge drinking, dirty talk, watching bad movies, encouraging others to sin, tolerating fornication, and other things of that nature.  That is the general principle of avoiding occasions of sin.  If they are necessary occasions of sin, such as a police officer speaking with prostitutes and criminals and going to the seedier part of town, they are not sinful.  If they are unnecessary and are proximate to sin, it is sinful to expose oneself to them.

I don't know your circuмstances and the occasions of sin for you -- only you know these things, -- but you can likely apply this principle to your situation.  Do not be afraid to be strict with yourself, either; the Sacred Heart wants to give you the gifts you need to finally gain entry to your true homeland of Heaven, where "eye hath not seen, nor ear heard, neither hath it entered into the heart of man, what things God hath prepared for them that love him" (I Cor. II, ix).

Second, always fulfill your duty of state diligently.  Avoid idleness, which is a lesser occasion of sin by which the devil tries to ensnare us into more serious occasions of sin (see first principle).  Go to bed early, wake up early, like Christians have done since the most ancient times of our religion.  Live an ordered life and, after you wake up (early), do not turn on the TV, check your email, get coffee, etc., but pray to God in thanksgiving for preserving you through the night, since He could have easily done the opposite.  Then say your morning prayers and make your morning offering (renew this offering if you commit a deliberate venial sin later in the day) and, before anything else, write down the agenda of your soul for the day.  We only have so much time, and we should use it combatting our selves so that we might be dissolved in the Lord and not fall into the pit.  Remember :  You are baptised, and thus you are dead to this world, being claimed by the Great King, who wants to protect you in His service.  Your life, your true life, therefore, is secret in the Lord, and it exists in fulfilling your duty, in prayer, and in the sacraments.  All else is superfluous, including the esteem of false friends, the esteem of non-Catholic/heretical parents when it comes to questions of our souls, the self-esteem that comes from thinking that one is admirable or is engaging or participating in something special that places him at a privilege in comparison to others.  If this special behaviour or skill or event or knowledge or personality quirk that is so great and in which one takes so much pleasure in thinking that he is distinguished above those around him because of it is truly good and worthy of esteem, we can esteem it in a way that brings true humility to ourselves and increases our love of God, recognising that it was made by God in order to bring glory to Him and that, therefore, it does not belong to us.

Now, I am just a layman in my early twenties, but I have had similar problems to you in my past life, and these are the lessons that helped me.  I hope that they will help you.  If you find them unhelpful, do not be afraid to ignore them, since they are nothing but the advice of an inexperienced, sinful layman.  I can say, however, that they come from the sermons of priests, from parish retreats, and from spiritual writers.  If they are truly helpful, remember that it is the means by which God is visiting you now and pray to Him for thanksgiving.  Take it as you will.  And, of course, if you still can, please go to a priest for counsel; giving medicine for these spiritual illnesses is his job.

  As a side note, not to disrupt the topic: getting dissolved in The Lord is not catholic idea. It is for charismatics and dervishes.
  God Bless.