L.
In a few months you will have a toddler who will stand and shake that gate, so you really need one that screws in. Could you mount it to the wall (in a stud) on the top or 2nd step? or maybe just behind or in front of the moulding? If there is a hall leading to the stairs, you could also gate off the hallway rather than the stairs themselves. This is what we did in my back entry.
Do not use a pressure gate, it would be very unsafe!
Good luck,
L.