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 the Electrum is installed and then sign the transaction and transfer it back to the online device and go to
https://coinb.in/#broadcast to broadcast the transaction.
Just as hosseinimr93 commented before, yet an offline and online devices are needed. Offline for signing message while online for making PBST (which is the unsigned) transaction which is signed by offline and broadcasted online. This would be a good suggestion for OP.