You do not have to use myTrezor with your Trezor hardware wallet. At the moment, there are a handful of wallets you can use with your Trezor. The software wallets that work well to an extent are Electrum 2.0, Multibit HD and Greenaddress.it. There are other software wallets that are planning to support Trezor such as Armory and Bitpay’s Copay.
Electrum happens to be my wallet of choice because it has a lot of features. One of the most important feature Electrum has in my opinion is the ability to use a passphrase with Trezor. Using a passphrase can be risky, because if you forget your passphrase then you lose all your bitcoins, there is no to get them back. Using Trezor with software wallets is quite easy, easier in my opinion than setting up a new software wallet as the Trezor holds all the important “stuff”.
Initialize the creation of a new wallet
Select the type of wallet
Choose Trezor and Electrum will close, once you reopen it you should be able to use your Trezor with Electrum. Give Electrum a little time to sync up and you are good to go.