Middle School - Flexible seating

I am interested in adding flexible seating into my middle school classroom.

Flexible seating can add a wrinkle to classroom management, but with careful planning and clear expectations, our students will rise to the occasion and use flexible seating to improve their own learning environment.  (edutopia)

Flexible seating options include:
-Working at tables or traditional chairs with attached desktops
-Standing at bookshelves or tall tables
-Sitting on gaming rockers or stools, or on carpet              squares on the floor or outside on the ground (weather  permitting)
-Sitting or kneeling on pillows at low tables
-Sitting on soft seating, bean bag chairs, or couches
-Sitting in lawn chairs with lap tables
- Yoga mats or exercise balls

While inspiring freedom and responsibility to students they will choose their seats best suited to their learning. If the student is comfortable they are more willing to listen and retain the information being given to them.

I am almost done with my first year teaching and there are SO many things I would like to add/change. This is number one on my list! 
PLEASE help me reach my goal!

I am planning on spending $300-$400 of my own money. The materials for flexible seating tend to be expensive! Beanbags alone are almost $100!

Thank you for your consideration!