I keep my patterns in a filing cabinet. If I can't get them back into the envelope, and for any patterns that I make, I put them in a manila envelope with the drawing or original package taped to the front.
Here's a tip for a pattern you use frequently-- you can get Freezer Paper at the grocery store and iron it to the back of your patterns. Use a pressing cloth or you'll ruin your iron and board! It sticks to the pattern and reinforces the flimsy pattern tissue. I never cut away any sizes so I can make it to any size I need.
You can get a basic pattern drafting text book to learn how to add ease and size up and down patterns and how to change them from one style to the next. You can't just take off 2" all the way around and expect it to fit.
I am a professional costume designer so your project will be completed with the best details and materials possible for your budget. You will feel all powerful and fabulous wearing a DeAnna Designs costume. It will fit you and be comfortable. Please check out some other costumes I've made here: