What you could do is to try to use tool such as: https://coinb.in/

I've been using it for quite some time and so far my keys are safe with me. What is coinb.in anyways? It is a website open-source that have basic functionality of signing an address and creating and managing transactions in general.

I use LIVE OS installed on my USB for this because every time I use this USB it is only existent in my RAM. Basically you want to boot up your live OS, download coinb.in pull the information about available inputs via some available block explorers out here and simply go offline after you get your inputs. Plugin other usb with your priv key or you can install software that can read QR from your camera codes before you even go offline and can read your private key this way. Sign a message with that private key and simply save your hex encoded bitcoin transaction either on your hard drive or plugin another USB so you can simply broadcast that hex later on.

I found this to be effective thing to do for me, might be a bit complicated but so far it have served me well.

I don't really see an other offline solution as you will still have to pull unspent inputs from somewhere.