I got some step-over gates at PetCo, not very expensive, made of wood. They are about 18" high. Holly has yet to jump over it and if anyone could, it would be her.
I also have the kind you install on the wall and it swings open and latches shut. I like the step over ones for places that you go in and out of frequently. With a step over type, you would not have to worry about your boys forgetting to close the gate.