This is a good post, I think I had a similar experience to you in that I had decided I wanted to start living a Christian life for a long time but I never got around to seriously doing it until about two years ago. I was raised nominally Anglican, and then converted to Orthodoxy.
I think the most important thing to begin living a Christian life was living a sacarmental life, which may e difficult if you are not part of a church but even the act of going to church and praying will be enough.
In Orthodox Churches the role of the Priest is as spiritual father and therefore is there to offer you guidance on your sins, and how to best resolve them. If you start attending you should ask for a prayer plan.
This is a central part of Christianity, and does not exist within other denominations short of individuals speaking to their priests of their own admission. Not as part of ordinary and necessary church life.
If you want to do something yourself before going to church, try reading a Psalm a day. Either Psalm 4 ("Answer me when I call..") or Psalm 50 ("have mercy on me o God…". Even praying twice a day, once in the morning, or in the evening will have a significant impact on your sexual sin.
Sexual sins from experience are a result of addiction to masturbation where you can go to more extreme things after doing it a lot. At least try limiting yourself, you should stop immediately; but in reality stop watching porn or even just extreme porn.
There is a lot of guidance on this.