How to use a 12.4 inch tablet while sitting?

I have a new 12.4 inch tablet that is perhaps a little too big.

I use it while sitting in a chair, but it needs to be tilted so I can see the display optimally in portrait format (around 30 degrees of tilt would be ideal), and it needs to be on a non-slip surface and not just wobbly resting on my knees.

Would a slightly smaller device perhaps make more sense for my use?

But my primary concern with this question is finding the optimal base.