It sounds like me last year. Constantly cleaning, organizing, wishing for less but kept buying more.
In the past, I would spend months trying to sell items on Craigslist or ebay. What didnt sell, remained. It was such a time consuming process that took a majority of my time. Then, like you, I would compulsively shop and not even want the packages by the time they showed at my door.
I realized I was addicted to the shopping cycle. I actually had to adopt a "one day at a time" philosophy to break it. It was such a part of my daily habit and emotional make-up. I think because we live in such a consumerist society that the few people I tried to explain this to didn't get how debilitating this was on my life. They couldnt see that buying things can be an addiction the same as drugs. They say that addiction is having too much of what you dont want - that was me.
As far as being attached to baby items, I cut swatches from alot of my baby clothes to someday make a quilt out of. The box takes up less space.
The feeling of just showing up at the goodwill with a van full of items is freeing. It feels good to give away to people. Once you start, it becomes so much easier! I have reduced my clothing by 50%, kids toys by 75% (and noone has ever asked for the missing toys- they didnt even notice!!), household items brought to manageable levels. What I ask myself when getting rid of something is whether my life will be in any way less if I dont have this thing. Usually the answer is "no".
My ds is not onboard with becoming decluttered. He feels his things represent who he is- he views them differently. THere is nothing I can do about this other than give him his own seperate space for his stuff. I cant let that bother me. However, he doesnt object to me downsizing everyone else's things. He saw unhappy I was spending all my time managing our stuff.
Start small. Go through a closet and have piles for trash, selling and donating. My criteria was anything worth less than $10 was donated. Big items that sat on Craigs List for more than a month were donated.
Physical items are not worth you happiness!
Oh and something that really helped me was watching "The Story of Stuff" - its on youtube.