You have now learnt two types of chords (suspended and add nine chords) which are formed either by substituting a different scale tone for one of the chord tones or by simply adding another scale tone to the existing chord. You can add any note of the scale of the key you are playing in to any of the chords in that key. Each time you do this, it will change the name of the chord, but knowing all these names is not essential for now. The best thing to do is experiment and memorize the notes and chords which you think sound good together. The example below is in the key of E minor and contains various scale tone additions and substitutions. Learn it and then use the ideas to make up your own progressions. With the knowledge you now have, you will be able to play hundreds of songs, as well as writing your own. You are well on the way to becoming an excellent rhythm guitarist.