Redwood is more durable and wera-resistant than white, so a better choiceI found a builders merchant online selling Redwood that seams pretty reasonable
When dealing with merchants what you need to as for is the "finished size". Redwood ex-6 x 1in will generally finish around 144 x 22mm, white wood would be a millimetre or two smaller - be very aware that there is no absolute fixed standard in terms of the finished sizes, so one yard's 6 x 1 could finish at 144 x 22mm and another might be 140 x 21mm, hence the need to ask for the finished size. Being slightly undersize in thickness isn't too much of a problem as you can always add packers (plastic horseshoe packers come in 1, 2, 4, 5mm etc - hardboard is about 3.2mm) to the tops of the joists to bring a 20mm thick board level with existing 22mm or even 25mm boards (this makes for a flatter floor and you also avoid any dip telegraphing through your carpets, as it invariably does) - being undersize in terms of width is more of an issue, hence my earlier comments about the usefulness of having a portable circular saw to resize boards to the required widthI measured this morning and found 2 different sizes, I think an area was more recently replaced. They are 6 x 3/4 (so 6x1 i think), and 5 1/2 x 20. I assume that slight difference in thickness would be okay under a 6mm board and underlay.
Make sure you get the rip fence with it - kind of difficult to saw a straight line without a rip fence!A friend has a circular saw that I will borrow.
Make sure you get the rip fence with it - kind of difficult to saw a straight line without a rip fence!