home experiment - How to measure amount of oxygen (or carbon dioxide) in air?

I'm not chemist, and I'm looking for easiest way to measure how much oxygen plant in closed container will produce per hour [can measure over time for increased accuracy].

My first idea was to measure percentage of oxygen in air with automotive lambda sensor.

However I don't expect good precision of measurement like this, and this is a little complicated (lambda sensor needs high temperature, so I need to heat it up).

I wonder if there is some chemical way to perform measurement like this.