Yes, you can use thermafleece insuation in a bathroom.
Before starting, look for signs of moisture like condensation, leaks, or mold. Addressing these issues first will help prevent future problems.
1. It is very important that there is a suitable vapour control membrane installed on the inside of the walls if insulation is to be installed in a bathroom.
2. Care should be taken that there is sufficient space above any insulation in the ceiling above to allow moisture that may pass through the insulation to vent.