The thing is the Trezor hardware wallet is not an airgapped hardware wallet it requires an internet connected wallet like electrum the only difference is that it doesn’t share the private key with the connected wallet which makes it safe so all this going back and forth between two electrum wallets is still same thing with Trezor, just connect it to an online electrum wallet and that’s all, you can still have a watch only though but it’s not needed in this setup.  But if you’re going in for a maximum security then go just use the electrum wallet on airgapped device and create another watch only device for broadcasting of transactions, this setup doesn’t need a Trezor or any other hardware wallet between them.