Hi Elaine,
I am anxiously awaiting the arrival of the CTX series as well. I have 'the Firm's signature Fanny Lifter' of their BBS1 infomercial fame. It is 14" and most people here are using roughly the same height, give or take a couple of inches. If you don't have this, you could use a stool, a chair, the end of a coffee table, or if you have enough risers, a regular step. There is information on the home page of Cathe's site for a mini step with risers. I don't know if it is available yet or in the works. This would be handy as regular step risers could be used and you could adjust it to whatever height suited you.
HTH,
Sabine