Absolutely nothing wrong with starting to write a song like that in my opinion. When you have that spine, you can start to vary the chords inside the bars by
* creating inversions with the bassline: for example, say you have a progression IV-I in C major, so there's one bar of F and one of C. In the first bar, instead of using just a whole note F in the bass, write F (half note) A (half note), or even F (whole note) A(quarter note) B(quarter note), so you get a little melodic line in the bass.
* thinking of the highest voice in your chord progression as a melody line. You can later move this to another instrument if you like, or just keep it in the pad/piano/whatever as a sort of counter-melody.
* "visiting" other chords during the bar: let's say you have that two-bar IV-I chord progression. Inside the first bar, you could write a small sub-progression IV-I6 (so in C you'd have an E in the bass)-IV
* varying the rhythm. The chord doesn't have to change on the first beat!
Also, check out the other threads on this forum about the topic, I think there's already a lot of good info about the theory behind chord progressions.