I put indoor-outdoor carpet in my room. It is very low pile, gives the warmth, but does not hide pins, etc. I use a lightweight stick type vacuum, which does a great job with threads,etc. Only problem is my little doggie, who loves the carpeting (but not in good way) so have to put gate up to keep her out. I probably would not put carpet again because of that.

I have carpet in my current sewing room, and I hate it. The dogs get hair all over it, the pins disappear, I can't lay my stuff on the floor without getting dog hair on it, no matter how often I vacuum. My last sewing room had tile, and I loved it. It was a bit cold in the winter, but I kept a small space heater next to my sewing room to take care of that problem. You definitely want a smooth floor.