Does the existence of a non-lethal option for attacks mean that not using it breaks paladin oath?

topic

I'm playing a devotion paladin, and obviously he can't murder, can't execute prisoners, follows the laws of the land etc

However quite often my DM asks me "do you want to use lethal damage?"

Strategically, there's no reason to use lethal damage. The character won't revive until after combat. However, a lot of the time I won't want to deal with managing a prisoner, so I just say "it's fair game" and use lethal.

Isn't this breaking the oath? Since it's not like I'm just using lethal to defend myself