Replace chipboard flooring?

[JM2]

Hi. Not the first I know, but I have some very creaky flooring upstairs and have the opportunity to resolve this in one (upstairs) bedroom in the new year.
Poorly sourced, badly laid, possibly been damp (before ourselves) chipboard sections - unknown thickness and sizing at this stage. (When we first moved in I successfully (for about 16 years anyway) screwed down a piece on the landing as all the nails seemed to have missed the joists below!)
Anyway, the bedroom. I'm prepared to rip it all up as a slow project and was looking to fit some new floorboards up to the stud partition walls. Is this a plan or do I need to look at putting down chipboard sheets again (same if good, or replaced if cracked - a suspect the T&G are pretty much destroyed in places. If I'm careful, do I need T&G at all? How much might good floorboards cost me (materials) if the room was circa 3mx4m (I assume this devil's chipboard is a lot cheaper).

All input welcome - I'm just at the 'I have a thought' stage right now.

 

[Burnerman]

Keep the same thickness of materials if you can - to avoid any step where this room joins a landing or whatever.
Chipboard is fine so long as it doesn't get wet - available in 18 or 22mm tongue and groove. The 22mm stuff can have a waterproof coating.
With the floor up, consider any extra electric points or new pipework - insulate what is already there.
If you want to use floorboards, fair enough - but acclimatise them for at least a month before laying. You'll need to hire some cramps for relaying.
I'd screw new stuff down - saves vibrating the ceiling below!
Get your materials from a timber merchant rather than the usual sheds.
John