Fixing for ceiling pull switch

[stevec59]

I'm putting a pull cord switch in my wetroom, the problem is 2 fold,

1, It's a flat ceiling, so I can't get above
2, The hole that Ive made and put a fixing into is crumbling away.

How to I get around this? If I could get above I'd put a plank of wood, but that isn't an option, I could try and put a piece if wood through the hole that the wires are coming through that is pre-glued and place that where I need it.
I have got some of these:-

https://www.screwfix.com/p/gripit-twistit-plasterboard-fixings-acetal-plastic-27mm-10-pack/384fp

And the metal equivalent, but my concern is that the hole will just crumble even more.
I've used the sprung toggles before but not found them that great:-

https://www.screwfix.com/p/easyfix-spring-toggles-3-x-50mm-20-pack/7978x

Thoughts?

Many Thanks

Steve

 

[Ian H]

Could you put a dry lining back on through the hole then screw into that? It would give support all the way round.

 

[durhamplumber]

I would be more worried about the crumbling happening in my wet room.