I was in a similiar situation, and had to decide a bedroom or basement.. I picked basement. Glad I did. I do miss the natural light but .. there are more benifits. I had much more space. I could leave it in any condition and it would un-noticed. I had lots of lighing put in so its lit up brighter than daylight. A huge plus ... my big fuzzy buddy, loves it down there. In the summer its so nice and cool, and in the winter he lays on his bed. Another plus is that there is room to expand when I need to like when I am laying out a big quilt, or tossing scraps around. In my planning I had more than one wall that could all be used as design walls if I needed.
I did put in a small space heater to supliment the heat. But usually once the iron is turned on , I turn off the space heater ( its amazing the heat an iron gives off) Wearing a thicker sole shoe with a heavier sock helped to keep my feet from getting cold on occasion.
I love my basement sewing space as it has more "useable" flexible space than any other area of my house.