I can relate. I'm reformed. Over the years I've helped a lot of friends get a grip on this "Stuff" issue.
Start by watching a TV show about organizing, and note the steps they break the process down into. One of the most effective steps is to clear up the entire contents of a room, removing it without making any attempt to sort it, to a neutral working area. It helps th break the attachment to the clutter staying in place, just the act of moving it.
It will not FEEL that way as you contemplate it, but if you try it, and have friends bring you empty boxes and help you crate it all up, you will look back and see I'm right and that you feel much better. You'll be confident that you are better able to manage the stuff.
From there, you can sort the whole lot into basic categories. Each time you sort, you have to pick up and move each item, over and over as you break the broad categories down further. You will be surprised to find how quickly you become willing to let go of a thing you have picked up and moved 5-6 times. :~) Eventually a lot of those items become items you are willing to give away or throw out.
Another great tip is to USE YOUR TECHNOLOGY. Rent a big, roomy storage locker to be your work space, as long as you can find one where you are not committed to a whole year's rent. (Wait till spring weather for this one!) The first item to put in the locker is a cheap worktable and comfy chair, a couple of white sheets, some thumb tacks, empty boxes, some markers, and some white address lables you will use to label and re-label boxes. As you sort things, take digital pix so that even if you get rid of an item eventually, you can know ahead of time that you will always have the picture to remember it by. You also can take pix of items grouped and ready to box for longterm storage, number the box with the pix's automatic filenaming number from the camera, and know which box to look in later for items you intend to leave in storage. Treasured itmes you let go of can always be printed and framed for display, to make a permanent memento of dear grannies' afghan that you might have kept if the cat hadn;t made it smell so bad. :~)
If you cull and cull items, faithfully doing this, you will eventually get down to a much smaller number of boxes than you started with. At that point you can either keep the locker and start on a second room, move to a smaller one, or take it all home to a storage area you can set up, there.
Having moved the roomful of stuff offsite, you will have a nice empty space you can start over with where the mess used to be. You can use standard organizers' tips to arrange it and maintain it. You will not have to look at the mess, or live in it, and you can go work on it with music to listen to, in a place you can work as long or as briefly as suits you-- then loick it up when you've had too much and leave it all behind to another day.
For a simple, easily-maintained approach to paper organizing, see my post of a few weeks ago (?) about that-- search on my membername here on my post, to bring up my posting history.
Another great tip-- some days you will just not be able to think about what to keep, or where to put it. Don't waste your time on those days arguing with yourself, beating up on yourself about how bad you are, trying to persuade yourself how much you need to organize your stuff, or how you SHOULD do this or that. Nope, change your focus! Those days are Purging Days, where your goal is to compete with yourself to see how many trash bags you can fill up and how far you can throw them. Change the goal from whatever goal has you stuck, to a more do-able goal of Creating Trash. One day, for instance, I Created so much Trash that it filled a small construction dumpster. Instead of thinking, "SHOULD I keep this, or that?" I made myself think of it in terms of, "CAN I please stuff this into a bag?"