If you want to be completely secure, you should import your private key into an air-gapped device. Being offline at the time of importing the private key isn't enough.
And it may worth mentioning that, you will need two devices for making transaction from your paper wallet. One should be offline and the other one should be online.
I just want to add this as optional you can make an offline transaction using
https://coinb.in/#newTransaction and generate a raw transaction where you need to copy and transfer it to the offline device where Electrum is installed to sign the transaction and transfer it back to the online device or
https://coinb.in/#broadcast to broadcast the transaction.
Tested this on a legacy wallet I don't know if the segwit wallets will work.