Bouncy upstairs floor, how and who do I get to sort it?

[LOOPYLOU]

Hi, our house is approx 160 years old and pretty solid except one of the upstairs floor. It has floorboards and does'nt appear to have hardly any gap between it and the downstairs ceiling which has exposed beams. The floor has a real bounce and it's a bit of a pain because it also sags meaning it's not level which is a pain with some furniture. It has been like this for years apparently, should I be worried or just accept this as a character feature.
Any advice would be great,

[lindonmatthews]

Hi there,
I've found if you turn the long runs of joist into box section, this helps to over come the bouncing. You will to take some time out to lift up all the boards.
This means cut some timber that connects the joist to the other joist, in a 90% fashion, about 12" between each. It will start off looking like an 'H'.
Have fun