Actually, it is a Hopper Ball large enough for adults.
I ordered the pink one but it also comes in blue
Pink Hopper Ball for Adults
Blowing it up wasn't as easy as expected till I realized its pump just wasn't doing its job after about the 3/4 mark so I tried it with another pump and got it easily up to 27 inches. May shoot for the other inch tomorrow after trying it to see how it fits. Right now I believe it is the perfect angle for my knees.
Here's a photo of the much stronger pump and the set it came with:
I wanted to share a quick webcam video without moving around any furniture. When trying to get into position, I took quite a flop backwards but Arnica gel was thankfully right within arms reach and it did its thing. I had fallen backwards and slammed my elbow into the floor. I would have shown more in the video but after getting right back up on the horse, I wasn't throwing caution to the wind so the video is very tame.