To buy a hardware wallet, you need to make an official money transaction using fiat currency.
Are you speaking from personal experience or have you never visited any of the websites of well-known HW manufacturers and seen that they even accept Bitcoin as a means of payment?
Disclosing the purchase of a hardware wallet will also put your financial security in question. In addition, your hardware wallet can be misused while being sent by mail.
You won't risk anything if you pay in Bitcoin and use a PO box, it's certainly one option that everyone should consider. Also, if you have an official seller in your country who has a physical store, you can buy HW for cash.
In addition, the very fact that you have a Ledger or Trezor indicates that you have a cryptocurrency. This information can be used by attackers.
If you've used any of the methods listed above and you're not someone who brags about things you shouldn't, then you can consider yourself pretty safe. People really find all sorts of excuses not to spend $50+ on something, but when they lose their BTC they surely regret not doing it differently.