If you find "no problem" to be hard to say - or perhaps you feel it is hard for your listener to hear - then you could try "my pleasure". I made this small edit to my speech a few years ago.

I recently heard a nurse say, "It's my privilege" in response to a thank-you. This felt like a more heartfelt acknowledgement of the gratitude being expressed.

One might also experiment with "It's no burden", which seems to fall somewhere between "My pleasure" and "It's my privilege".