Poslaju.

Pos Ekspress can only be used if you don't exceed the weight and thickness as stated on the envelop. If not it will be returned to sender and your money spend on it is wasted.

You mean delivered via Poslaju?

When you post out your item, they'll most likely ask you to put it into their Poslaju plastic flyer. Or you can always ask from them. The flyer will protect it from getting wet and getting tampered with.

As for your condition of the items, clothings will be the least of my worries. Tons of clothes are sent via Poslaju everyday. I would worry more if it was an electronic item or a bottled perfume but clothes will definitely be fine. Some sellers just put the clothing into a plastic bag andden put the whole plastic bag into the Poslaju flyer.

If that's the case, then the best way is to put it in a box with protection. Take note of the box size, if its too big, they may use volumetric weight and it'll be very much more expensive. Poslaju also sell boxes that you can purchase to put your envelop in.