If you're mailing a sweater, then you're mailing a package, you shouldn't choose envelope even if you could.
The retail cost to mail a 1-pound package via Priority Mail is $8.70 - $19.40 depending on distance (Zone). If the package is under 1 pound (even 15.99 ounces), you can choose "First Class package" as your service (not package type) and the online cost will be $6.28 or less (depending on Zone and weight).
The enormous $19+ price for 1 pound via Priority Mail only applies for Zone 9, which is a few remote Pacific islands. If you're shipping to any US state or territory, including Alaska or Hawaii, you'd pay the Zone 8 price which is $11.60 for 1 pound retail Priority mail.
To avoid using the new listing tool (for now, at least), click on the 3 dots in the upper right corner of the listing form you're using now, and switch to the "business tool" (AKA advanced listing form). Ignore the pop up message about being a business.
