My sewing room for years was the entire finished basement. Sometimes we used a dehumidifier and sometimes we didn't. I never had a problem. Last summer I moved upstairs to a spare bedroom that faces north. I am so much happier now that I am upstairs. I didn't like not having windows or being isolated downstairs. My space has been drastically reduced, but it is so worth it. Maybe you could put blinds up to reduce the heat. Just make sure it is really what you want. It is a lot of work moving everything. Good luck in whatever you decide.