I do HODL my BTC in cold storage while I'd like to transfer them on my brand new hardware wallet.
But why? I'm serious: if your current setup is working and secure, why put all your eggs in one basket?
That being said: I wouldn't use Mycelium for any serious amounts, it's a mobile hot wallet.
The safest way would probably be to use a desktop wallet (e.g. electrum) together with an offline computer.
Download the original electrum and verify its signature. Then use an offline device (or a live booted linux distro in offline mode) with electrum to create and sign a transaction sending the funds to your hardware wallet.
Correction: you'll have to create the transaction on a hot wallet. When you import the
address, it downloads all transactions so you can create an unsigned transaction.
Then copy that transaction to your offline air-gapped computer running from a Linux LIVE CD, import the private key, sign the transaction, and copy the transaction back to your online system. The point of all this is to ensure your private key never touches any device that's connected to the internet.