I have seen some amazing wood decks done with paint, but when you get to larger scales like 1:200 nothing looks as good as real wood to me. Most ship deck planks seem to be somewhere between 4" to 8" in width, and as 1 mm works out to about 8" in 1/200 I would not call it hugely out of scale. 1/32" wide stock, which scales to about 6", is readily available from places like Kappler (http://www.kapplerusa.com/) and I have used it to plank plastic ships in this scale. Aside from the width of the planks it is also important to determine the length of the planks, how the joints between planks line up across the deck, and how deck edges, bulkheads, hatches and fittings were treated.
If you want to see one way it can be done, go to the Forums page at ModelWarships.com (http://www.modelwarships.com/), scroll down to the Online Scratchbuilt Projects and then find my article "1/192 HMS DORSETSHIRE Scratchbuild". Starting on page 3 you can see some photos of the deck in progress and an explanation of the process.