Bene
One prefix that I found that means "good" is "bene", as in "beneficial" or "benevolent". Or Beneful, if you like dog food.
The word "complaining" means to express feelings of pain, dissatisfaction, or resentment. As such, there are very few words that can prefix it. The only obvious one is "uncomplaining". Otherwise,...
anti
When I use a prefix before a word ,I double check to make sure it sounds right.