What kind of mask do I need for paint/stain fumes?

I make/sell home decor pieces and I do my painting and staining in batches 1-2 times a week. I usually do it outside, but it's getting really cold here, so I'm going to have to start doing it inside in my office. Is there a mask that will protect me from the fumes? Or is it a completely bad idea to do it inside? Even if I wear a proper mask, have the fan on, maybe window open, stay out of the room for a day or two afterwards.

I don't have a garage I can work in either.