Lip Trill

I just cannot do the "lip trill" exercise. I am doing NG instead having researched this problem on

internet. Is that a good idea or would you suggest something else?

That's a great alternative! 

Here's a lesson on other lip trill alternatives too: https://www.youtube.com/watch?v=0wzbyyl1d-I.

Here's an article on lip trills and a short lesson with extra tips as well!