If you buy a hardware wallet and connect it to their official companion software, you are trusting 100% in a single company. Instead, you can improve your security, and reduce your trust in a single company by using a third-party open-source wallet instead of the official one.
So, having a single device, as you suggest, is a very bad idea. You would be trusting 100% in a vendor.

The secure setup is:
* Create the transaction in an open source thirdparty software wallet
* Send the transaction to your Hardware Wallet, in an airgapped medium, like QR or sdcard
* Review and sign the transaction on the Hardware Wallet
* Send back the transaction (now signed) to the software wallet (with QR or sdcard)
* Broadcast the transaction