If you want a secure way to interact with these private keys that you have, then the best method is instead to set up a permanently airgapped device, format it and install a clean version of Linux, set up full disk encryption, and then install a wallet such as Electrum and import your private keys to it. Import the addresses in to a watch-only wallet on an internet enabled device to be able to generate transactions for your airgapped wallet to sign.

As others have mentioned, this is only safe if the private keys were generated safely in the first place - in other words, also on an airgapped device, using software you have verified, and have never touched an internet enabled device. This may be the case if the private keys you are holding are on properly generated paper wallets.

If you want to use a hardware wallet as intended, then once you have set it up simply sweep all your coins to new addresses generated by the hardware wallet.