Thanks for the tip with watch only wallet. The thing is - I also need to send bitcoins from Electrum. Would this cold wallet solution, perhaps with some modifications, work for sending or a completely different approach is neede then?
Sure, you can use your watch-only wallet to create unsigned transactions, then transfer them to your cold wallet for signing and back to your watch-only wallet for broadcasting.
Or, you can just install electrum on a 100% clean desktop PC that can actually connect to the internet, generate a new seed (write it down), export the xpub to your server for a watch only wallet. In this case, you can just spend your funds from the electrum wallet on your online desktop PC.. Offcourse, this setup is less secure than a real cold wallet.
A different, safer, sollution would be to use a hardware wallet and export it's xpub (and import it on your watch-only wallet on your server). This way, you could spend your funds by using your hardware wallet
