I don’t mean to disrespect your practice or to try to pull you away from something you are intent on doing, however I invite you to reflect on something: Physical/corporal mortification is something that is comparatively easy to do. Yes, it may be uncomfortable, or even painful, but it does not require a lot of effort.
What is difficult is psychological and spiritual mortification. That is, cutting off bad thoughts, negative emotions, and harmful actions. This is incredibly hard, since it requires a great deal of willpower and an enormous amount of vigilance (for if we fail to watch ourselves for even a minute, discursive thoughts can sneak into our minds). But remember that “every man shall receive his own reward according to his own labour” (1 Corinthians 3:8), and if you undertake this more difficult type of mortification–spiritual mortification–your reward will certainly be much more worthwhile.
Even Jesus said, “If any will come after me, let him deny himself, and take up his cross, and follow me” (Matthew 16:24). Spiritual mortification is denying ourselves, that is, denying our desires, our anger, our pride, our jealousy, our fears. But it is very difficult.
If you are the type of person who would consider a practice such as wearing a cilice, you obviously have a strong yearning towards holiness. But God is far more interested in having our hearts directed towards Him than He is in watching us undergo physical pain or discomfort, even for His sake. So my recommendation, if you have the inclination towards a deeper, more rigorous spiritual practice, is to direct that energy towards developing a tranquil and loving heart, rather than causing yourself discomfort.
On another note, if the discomfort makes you grumpy or irritable, and you thereafter interact with other people and spread that attitude to them, than you have certainly nullified any good you might have accumulated through use of the cilice, since you are spreading suffering in the world, and I cannot imagine a God who would look favorably upon that.
I don’t mean to preach at you, or to put you on the defensive about this practice, and I apologize if my words have had that effect. But I just think it’s wise to reflect on this issue, and I personally feel that a person’s spiritual inclinations could be directed to far greater ends.