I sanded and varnished white deal in our house.....in my opinion it came out very well. We put down(well me specifically!) 3 coats of light oak coloured Ronseal Diamond finish to give it a colour and 1 coat of clear matt varnish on the colour.....
Noise, not really an issue. We don't tend to have herds of elephants upstairs while we watch TV.
Warmth, the house is new, we have no issues with it being cold.
Gaps, they do happen....the boards shrunk notibly in winter, but hey, wood is natural and it adds to its character.
When i step out I of bed I have to say the wood is not that cold...wood is not the coldest surface i have ever walked on, if it freaks you out that much, keep slippers next to the bed.
The sanding and varnishing yes, without a doubt is tough. We have 4 bedrooms, it took the bones of a week on and off..
Ask the builder for an off cut of the floorboard....go to a few paint shops and ask the lads to dye strips of it, use the Ronseal Diamond coat, etc. You'll be surprised how it can look nice.
One word of warning...it is a very soft wood......protect the floor by using those plastic disc things that the castors wheels slot into...otherwise, they'll actually dent the floor where the wheels are on it