Ok, I don't know the song but I'll try to help you figure it out.
Looking at the chord progression I believe that the song is in A major. So to figure out a bass line you're probably want to stay in that scale, meaning that every tone that you play will be in that scale. This narrows the possible notes you can play from 12 to 8.
So the notes in the A major scale are A, B, C#, D, E, F#, G#, A
here's a fretboard diagram to show you which notes you are “allowed” to play in this song.
so my first suggestion is that you just go through the song and play the root notes of these chords whenever they change (A,E,C#,F#,B,E,A,A). When you've practiced that just listen to the song and start adding notes. Only add notes that are in the scale and it will sound good.
Hope this helps