Should I buy a pro controller for the Nintendo switch lite ?

You should buy a switch and then get a pro controller for that. 

You *can* use a pro controller or joy cons for the Switch lite, but it would be rather pointless. First of all the Switch lite's screen is very small so using it in tabletop mode wouldn't be fun. Second of all it would defeat the purpose of getting a switch lite- the cost of the original Switch is only a little bit higher than the cost of a switch lite+pro controller.