hole in floor: what to do

I have a cheap ip whose floorboards in the kitchen arent great. The tenant has fallen through

Im looking for an affordable fix

Tradie has recommended something from underneath and says it might to be too hard

We are thinking of putting yellow tongue over the top however that would mean having to todo the entire room which is quite large plus since everything would rise the doors would have to be shaved down as well

Is there any other ways or options for a fix??

Is therr such a thing as a sturdy piece of metal thats thin over the hole?
Thanks everyone

hole in floor: what to do