M.G.
I know you wrote in your SWH that you know about pressure mounted gates at tops of stairs. Friends of ours had a terrible accident, so I just urge not to go that route.
Here's what we did.
We bought the wooden kind that slide open/closed to expland. Click shut.
We used super strength plastic (hardware type) ties and attached them to the staircase with a block of wood. Hard to explain, but we didn't have to drill holes.
Does that stair case have balusters or newel posts? If so, you can attach a block of wood to the newel with these super strength hardware type ties (that cinch off so they cannot move), and you attach the gate to the block of wood with screws. So you are not screwing into the wall - but into the block of wood. You can Google this. The instructions came with our particular gate but this was decade ago.
Good luck :)
** When you take the gate down, you just cut the cinch ties and remove the gate from the blocks of wood. No damage to walls or stair case.
My husband put all his weight (with mine) and we rammed that gate - didn't move. Not even budge.