Instead of creating the transaction yourself, transfer the private key to a text file on a USB stick to place in your online machine. If you like you could turn off your WIFI at the wall to be extra sure. Then you can open Electrum and sweep that key directly into your Electrum wallet, reading from the usb (with wifi back on). Electrum only exposes your private key on your PC for a fraction of a second in order to sign the transaction for you, then broadcast it.
If there's malware waiting, the few seconds it takes you to broadcast the transaction is enough to steal your Bitcoin. And even if the malware is 2 seconds late,
Full RBF means you'll still lose your coins. There's no need to risk it, so keep private keys offline.