Depending on the color your going with on the exterior, if you keep it red or another darker toned color, I'd go lighter almost honey on the floors; knotty pine? I have always wanted to redo a barn into a modern/rustic home!

Thanks :) Yeah decided to go with tile. So sand cement is ok over existing tiles if I prep them first? Only problem is, the new pad can only be about 30mm at it's thickest (leaving up to 15mm for tiles) otherwise it'll end up being higher than the hallway floor. So I either need to make the fall shallower or not bother with the waste and make it all level. If I made it level, could I use levelling compound at that thickness or would deck mud/sand cement be the best option? Also, should I be putting in mesh for strength? (I know I should (and will) ask the local hardware what they suggest, but it's great to have suggestions from the Houzz community also)

We are a little biased, but wood floors are versatile, durable, clean, and timeless. Whereas carpet will eventually need to be replaced, high quality wood floors can last forever. You can install radiant heat under the wood floors if you are worried about them being too cold during certain times of year, and you can easily install area rugs over the flooring. Wood flooring is also more versatile than it has ever been so you can create any look. As an added bonus you can easily sweep and mop your wood floors, whereas with Carpet you don't always know what is lying below the surface. Good luck!

I think it would make both rooms too dark. Maybe go with a lighter floor colour?