I have similar sets of stairs. We used multiple gates to block them. I have the extendable ones that fit different lengths and are both pressure and mounted from First Years.
The one mishy has is called cosco configure gate and it is awesome. You can buy extensions to make it as long as you need it and it bends at the joints so you can make it go from wall to wall even if they arent perfectly parallel.
Did you by chance mean Kidco? I can't find it under Cosco
Re: baby proofing question
I think it is Munchkin brand from BRU.