Check Big Lots for kids' chairs. They sell kid lawn chairs for less than $10 and kid-sized saucer chairs for $15.
I used to have bean bag chairs but recently switched to a saucer chair, a cushy rug, and a little side table ($13 at WalMart). I added a lamp and plan to have my kiddos bring in framed pictures of their families to put on top of my bookcases. My room is also super tall, so I want to hang some paper lanterns (Dollar Tree for $1 if I can find them again this year...otherwise, I'll get a set from amazon) to bring the feeling down low to make it cozier... I LOVE my library...it's my favorite place in my classroom!