How to keep clothes in other sizes
Do not save any clothes that are worn out. The maternity pants that you wore every day during those last weeks because they were the only pair that still fit (and therefore have drops of chocolate ice cream stains on them, not that I am speaking from experience or anything) can be thrown away.
Go through them every year or so to see if you can size down your collection. Even classic styles can change every five or seven years.(Think how different denim looks now from a few years ago.)
If you think it not likely you will wear them again, do not save them, but do not be afraid to set clothes aside in case you can wear them in the future. That kind of the whole point of storage space using it for good, not for clutter.
ou want to keep them in a box in your storage space, not in useful closet space with your current size.
Keep only the clothes that you will be happy to see again. Keep the best stuff, not everything.