The original way is bass, DU,bass,DU.
as a begginer the bass note is kind of hard to pick the right string and still keep the rhythm going on the strums.
I suggest instead of playing the bass note, replace it with a down strum. so it would be D,DU,D,DU. it will give you the same overall rhythm and be easier to sing along with. (don't give up on the bass strum though, keep practicing that. It is used in alot of songs so is a good thing to be able to play.)