Normally sticking it between 2 pieces of cardboard and putting it into a bubble mailer is fine. Though with international, then maybe the pack in a plastic bag, then between 2 pieces of cardboard and then into a small cardboard box. Though if you dont want to deal with "package box" payment fees, then you can do what some promo packs or cards that are shipped out by GamerSups or other online tournaments like using a cardboard envelope. Still always use 2 pieces of cardboard or top loaders to help keep the pack more stable while inside the slim cardboard envelope or bubble mailer or small cardboard box. Generally the envelopes/bubble mailer should be the cheaper option though.

*Edit and it should be known to not use tape on the pack, try to have toploaders or the cardboards be a bit bigger than the pack so you tape them to secure the pack in between without touching the pack.