My house has walls that are like yours. I have used the plugs that you describe to fix curtain rail battens to the walls, and they are pretty good fixings. You can get those plugs in plastic and in metal. The plastic ones are best for fixing to a vertical surface, because the shank, or body, of the plug fits nice and snug in the hole that you make in the wall. There is a really strong fitting available for studded [hollow] walls, and that's called an Interset fitting. It is [or was] made by Rawlplug, and it will take quite heavy loads. I fitted a bathroom cabinet with 4 Interset fittings, in 1995, and it's still there!