Does this sound natural?
Uncomfortable = 気持ちよくない
I want to say: This chair isn't comfortable. May I please change it?
Is my sentence ok? Is there another way you would say this? Thanks!
This is going to be a bit advanced. In Japanese there is a word for "comfortableness": gokochi - 心地
So for "this chair isn't comfortable" you could say:
suwarigokochi no warui isu desu no de, kaete mo ii desu ka?
With gokochi, you need some verb, and in this case it is "uncomfortable to sit", so suwarigokochi ga warui.
For beds, you would use 寝心地 - negokochi