Relax as much as possible when you fret your chords. Also, be careful that you’re relaxed if/when you slide up or down. Slides are harder on the finger joints than normal fretting.
If you don’t already do so, use coated strings. They’re easier to slide around on than uncoated strings. Get your guitar set up so the action is as low as possible, using the lightest string gauge that still works for you.
Playing in “c” is more difficult than playing in “G”, because you won’t be able to use as many open strings. So try to play as much as possible in the key of G. Relax!