I use an old "ornate" arm chair that used to belong to my great grandmother. It fits in a formal living room as it looks nice, but it is padded enough to be very comfortable for long hours, but light enough to be moved around for lessons and normal living at home. Something similar to this:
Surprisingly similar in style and color too! I recommend Craigslist or antique shops for finding something affordable. The ONLY drawback I have to this chair is that there is quite a bit of sentimental attachment as is belong to my great grandmother, and young students like to bounce on it when we switch places for me to sit on the bench during lessons. smirk