getting mini computer as a wallet with electrum

I am planning to get some raspberry model, permanently get rid of internet connection and use it as a airgapped wallet with electrum and sign the transactions with usb. Is it a good idea? I feel like it's more secure than using a hardware wallet such as trezor which has higher chance of having backdoor. What are your opinions? Which raspberry pi model would you recommend or any other device? I don't want to go as far as building the computer from ground though.