Questions about Tunturi Gymnastikball reissfest ABS Anti-Burst

Is there a protective cover for this product? Because I would like to use it mainly as an office chair.

What kind of valve does the ball have and how often do you have to inflate it?

I have just received the 65cm ball and wanted to use it as a sitting ball for work. However, it is much too low (it measures less than 65cm in diameter, oddly enough). Is the 90cm ball better for a body height of 175cm?

Is it 65 cm in diameter or circumference?

Is this made in China?

With a height of approx. 180cm, which size of ball do you recommend, 75cm or 90cm?

Does the tunturi balloon contain phthalates?

What is the right size for sitting at a lectern.