Certified mail is tracked.
As to sellers, First Class, third class/merchandise enclosed can also be Insured which tracks the item, indemnifies the item and is less money at $100 than Certified and just a dime more than certified for $200 coverage.
First Class packages is harder to answer since zone (distance) and weight, in ounces, create may cost levels.
Go here: https://pe.usps.com/cpim/ftp/manual...otice123.pdf
for the current Rate Notice 123
AND here: https://pe.usps.com/resources/Price...otice123.pdf
for the new version for rates beginning Jan. 22, 2023.
You can get the updated versions (as well as older ones) by just searching for "usps notice 123 pdf" and to be more specific you can add a date, such as January 2022, October 2022, 2023 or the like.