Three suggestions:
1. Capo up to the fifth fret. Now to play in the key of G (chords G, C D7) you will finger chords in the D (D, G, A7) which will sound in the key of G. However the inversions will be different and the whole sound of the guitar will change as you capo.

2. Some nice chords. To sound a bit more folky explore suspended chords. These take out the the major/minor third and put in the second or fourth note instead. Some simple examples. Leave the E string unfretted on a D chord - that's a Dsus2. Put your little finger on the G note instead of the F sharp (2nd to 3 fret on the E string). That's a Dsus4. Slide a C chord up a whole 2 frets, leaving the G open on the 3rd string. That's a Dsus4 as well (a favourite sound!) Finger a G chord with your second, third and fourth strings, and put your first finger on the C on the second string. Thats a Gsus4. Take your first finger offthe second string in an Aminor chord and it becomes an Asus2.

3. Don't panic about 3 chords. 'Blowing in the wind' only has three, so does 'Dark End of the Street', 'Grand Coulee Dam' and 'Sloop John B'......

cheers
KP