Been there, except I fell through and landed up on the bathroom floor, after feeling 'lucky' I had landed in the only area on the floor that didn't have the washbasin, loo, bath, or shower I found I was straddling the electric cables! Got a local plasterer to quote and he sorted it out for me, patched up the holes with new plaster board and reskimmed to blend in, brilliant job, then I just painted. (I fell through as I was catching mice and heard the humane trap go off, clicking away, I didn't want poor mousey to be in there for any longer than necc, so dashed up to retrieve the trap and promptly fell through the plasterboard, mouse and all. Mouse was fine btw!). Get a reliable person in to do it all if you can. Ask around for recommendations.