This is my second trip to Bad Kreuznach, and both times I've stayed at the Furstenhof hotel, which…read moreis right next door to the Crucenia-Therman. The hotel gives you a voucher for 10% off the admission fee. Unlike most Therman Spas in Germany, this facility is not textile free. However, I read online that the sauna areas may be the exception. Also, unlike other spas, they do not issue you a wristband with a Bluetooth chip that is used to lock/unlock your locker. Instead, you use a one euro coin that unlocks the key, and you receive it back when you leave.
There is a large pool that has an indoor and outdoor component. I was there in the morning, and there was ongoing aqua exercise classes. However, you can certainly swim around them as most people were moving in a circle. This is a very relaxing leisure activity with pools, classes, etc.
I would recommend the Crucenia-Therman over the Baderhaus only if you are hesitant to go "textile free".