It is awful to downsize and get rid of all your treasures. Start by keeping those things that you cannot replace. Keep the things that you use daily. Good luck with the rest. I did it and now I am building a barn 30x50 with the first 20 feet my room for sewing and fabric storage. I hated it not having space to sew and always having to dig for fabric when I wanted to make something. At times I would get so over whelmed with my search I would just forget it.
Good luck with your move.