International cargo

Are you looking for a logistic company or courier. You mention you have to ship some small packages. If it is not time sensitive I would always choose ThaiPost. The customs process is easy and usually they do not charge any fees on top. On the other hand on arrival the change is high that no import duties have to been paid. Other option would be to send via FedEx, UPS or DHL. Those are courier services. They pick up you packages or you can bring them to their service stations. You will always have to pay duties and taxes for import and usually a service fee for customs clearance and you will require to ship via a registered company. Post and courier have restrictions on what can be shipped.
Using a logistic company for small items might be the most expensive solution as everything is usually charged extra (pick up, customs clearance for export and import, handling fees, etc.) As well most of the logistic companies will only handle your shipment if you have a registered company in Thailand.