Is it really all just luck? I have heard that there is a guaranteed heirloom after 500 packs, but I've opened a bunch- I don't know how many. Still, I was wondering what I can do to raise my chances without wasting all my money.
If you are looking for the easiest way to get a heirloom of your choice, then just buy 500 boxes and you will for sure get at least 1.
If you don't want to spend 500 eur on a heirloom, you can also wait until an event with a heirloom is live and craft/buy all 24 items to get a guaranteed heirloom.
If you don't want to spend any money to get one, then it's just pure luck. You can create a new account and try your luck there. The first levels grant you loot boxes like crazy, I know a guy who got a heirloom on his alt account, which eventually became his main.