Hi Phil,
the chord shapes that you're using are good ones - if you're playing a three note chord, the fifth is 'generally' the one to leave out (unless you particularly want it there) - partly because unless it's altered, the sound of the fifth is so familiar that your ear will fill it in anyway, and partly because, to assist us in doing that, it's the second harmonic of the fundemental anyway, so it is there in the chord, albeit in a subtle way.
I'd suggest experimenting with putting fourths/seconds/sixths into chords, in different combinations with or without the other chord notes - R,4,5; R,2,5; R,5,9; R,5,6; R,2,Maj7 etc, and then stretch them out over four strings.
I could write them out, but that would rob you of the fun of working them out!
have fun.
Steve
www.steve-lawson.co.uk