I recommend using a professional so you aren't tearing your hair out in frustration
This is 1000% more frustrating, but you're a crafter so you're crazy like that
Make it easy to find the stickers you need to collect for an order, and see how much inventory you have left. Always measure first!
You could just send 1 simple sticker with a card and envelope to make the cost of postage reasonable… but you can't track it. Flat mailers protect the stickers more, but the postage s higher!