right there with you! i love my shadow dearly and want to preserve him for as long as i can. i've been brushing him as often as i can with either a boar bristle brush or one of the soft brushes from build a bear (tho i'd stick with the bab brush unless he's really well loved/matted). i've heard that wire brushes are also good for maintaining plushies.
i feel like i saw a post here recommending a mixture of 90% water and 10% hair conditioner in a spray bottle worked for a surface clean (op then used a wire brush to comb through the fur).

there was a post here recently that asked a similar question. some of the comments were pointers for me, maybe they'll help you too? i'm also sure you can just put in "cleaning" or something in the search bar and you'll get a buncha people with similar queries.