I looked into the prices of the Tumbleform seats and came across the Special Tomato Sitter at adaptivemall.com. It was cheaper and it had more benefits than the Tumbleform seat.
Not only does the sitter come with a nice wooden base, it can also be fit with wheels to allow us to move the chair easier.
And what really sold it for me was the option that I could take the seat off of the wooden base and strap it to the kitchen chair. I can use it for a high chair at the table or for him to sit at the table and have a large area to play.