My husband is diabetic and loves potatoes which are not good for him. I have done this and they are very good. You steam the cauliflower then mash and add whatever you would to mash potatoes. I add butter, sour cream, cheese, chives, salt, pepper etc. You do need to drain it well since cauliflower does have more water in them than potatoes.
Give is a try and don’t tell anyone and see if they notice the difference!