I also tend to keep and reuse decent quality inner sleeves, rather than replace them with new MoFi sleeves, (like I do with the crappy cheap paper sleeves that come with some LPs.) However, if you wish to keep the inner sleeve because it has decorations, or lyrics, or whatever on it, my suggestion is to use an outer sleeve bag, and merely put the inner sleeve along side the LP inside the bag. That way you'll never lose it.
My two cents worth.
My two cents worth.