Adjustable height office chair. (Cornton FK9)

We are looking for an adjustable height office type chair to use at a table. The Ukrainian lad who is living with us is working at a computer remotely with Ukraine for at least 4 hours a day and is getting neck ache using my dining chair! If we can find a chair that we can adjust the height of to fit him, it would be great. I can collect it if that helps.
Thank you for everyone’s generosity.

       
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