I use a lot of 12 x 15.5 Tyvek envelopes, my go to packaging for shirts which weigh in at 13 ounces or less. 4x4x4 boxes are great to have on hand if you sell a lot of ties. I buy these from ULine, but IIRC ebay can be a good source, particularly for smaller quantities.
If I could only give three pieces of advice on shipping they would be:
1. If it's 13 ounces or less, ship First Class Mail.
2. Buy a scale and compare the Priority Mail options. Newbs tend to use Flat...