We use dream baby gates. You can purchase extensions so they can fit most gaps.
They are pressure mounted, but you can screw a cap onto the wall for extra safety if you want too (we dont bother)
Ours looks like this (you can also get them at one metre high and they come in black or white)
They also self shut, which is handy when you have your hands full .. you can get them at babycity, the warehouse and baby factory.