Line Floor before Carpeting?

[mcprinter]

1930s House. Upstairs Spare Bedroom.
Not been touched for 20+ Years

Quite a few damaged Floorboards from Plumbing and Electrical Work over the Years.
I have replaced some of the Boards with 22mm Chipboard. Screwed loose ones down.
Still left with a few Gaps where the Tongues have been cut off. I can see the Ceiling below through them.

Should the Gaps be filled? If so, with what.

The Floor was lined with Brown Paper under the Underlay. Is this still done? Anything more modern?

Fairly big Room 5M x 4M. Don't really want to Hardboard/Ply over it.

Thanks

 

[Tigercubrider]

People used to use newspaper to block drafts this was replaced by stiffish brown paper, it also has the benefit of stopping the cheaper underlay sticking to the boards.
I’d use it.