Best way to keep mice away?

We’ve tried glue traps, mouse poison, and the snap traps and none worked! We got an exterminator for a year but our contract is almost over. We can’t afford to buy them again and their services worked for most of the months until recently we seen some droppings and a mouse running. All they did was put mouse poison in the house so I think whatever brand they use worked for awhile but not now. (Orkin) I got two very young kids and don’t want those nasty things in my home pooping and peeing on everything and risking them getting sick. What else can I do? Will a cat help? (Of course we’d love it and take care of it and make it part of the family)