I tackled the same problem myself a few years ago after initially approaching a carpenter. His price was too high as he said he didn't really know what he was dealing with until he started.

I put it off for ages for fear of lifting the carpets, which weren't very old, but then had to get some up for electrical work anyway, so bought a carpet kicker and bolster from homebase to put it back down after and wondered what all the fuss was about!

The creaking in my case was a mixture of plywood having been overlaid in one place but generally loose nails. I bought a large nail puller and used screw-tite screws, 50mm I think, and replaced loose nails with them or put them right next to tight nails. Main thing is to check there are no cables or pipes if not using the nail holes or using screws longer than the nail that came out. Mine are creak free years after.

However that's with normal floorboards/planks. The newer side (extension) still creaks but it's chipboard which is harder to deal with. I had some success in one particularly bad spot by cutting the tongue but haven't tackled it more widely yet.