To reiterate, I’m after sending a 1st class piece of mail, with tracking.
So, are you still asking for an answer from us? Or did you figure it out for yourself by going through the flow chart you posted?
The straightforward, simple answer is, if you want a tracking number, you have to buy ‘first class parcel’ postage.
What may be confusing you is that there are three different types of ‘first class mail’, so when you use that term, people have to make assumptions about which one you’re talking about. The three are:
- First class letter (does not include tracking)
- Large envelope/flat (does not include tracking)
- First class parcel (includes tracking)
First-class parcel, which includes tracking, is the most expensive of the three. First-class letter is the least expensive, and large envelope/flat is in the middle.
If your goal is to send a package with a tracking number, your only option is to ship it by first-class parcel.
If your goal is to save the most money, and you don’t care about a tracking number, then you have to go through the USPS flow chart to see if your mail piece qualifies for either of the lower first-class rates. If it does, great, you’ve saved a little bit of money, but you won’t have a tracking number.
Since your stated goal is to have tracking, just ship it first-class parcel, which is the ‘first class’ that is available in Amazon’s Buy Shipping system. You don’t need to do anything special to your envelope to make it ‘qualify’. USPS doesn’t care if you send a plain old envelope using the more expensive first-class parcel service.
Technically, if your small envelope is less than 1/4" thick (question 4 in your flowchart), it’s considered a letter and, if you are really concerned about it, you can stick a piece of cardboard or some folded paper in the envelope to get it over the 1/4" thickness. But USPS will almost certainly not care, because you’re paying more than you’re required to (using parcel rate to get the tracking number, instead of letter rate which your item might qualify for, but doesn’t have the tracking you need). People rarely object when you give them more money than you have to, so don’t worry about it.