One way to be happier and find more balance is to find the open door (or window) of the conversation or request. If you feel like you say "no" too many times, this is the perfect opportunity for you. It doesn't even take extra time!
The open door (or window, depending on the options available) is giving another option of when that person or child can do something or have something, even though you're telling them no.
For example, your son asks you if he can have his sucker and it's ten minutes before dinner time. Instead of saying "no, you can't have a sucker before dinner," you can find the open door and say "you can have the sucker after dinner" or "you can have this glass of milk right now." Another example is when your partner wants you to run an errand - instead of saying "no, I don't have time today," figure out when you do have time and say "sure, I'll do it after work tomorrow." In both examples of the open window, you've provided opportunities to say yes, or options where the person or child is able to have something they asked for or want.
Providing an open door or window means saying "no" less often and giving options that make it easier for the person to accept your decision. This concept also allows the word, "no" to remain important for those times that require a firm no. You'll find that over time finding the open door becomes easier for you and your family will be happier with all the positive options you're giving them.