Wow, that's a tough one. I would go with wide, padded leather restraints for bondage. The wider the body area bound and the softer the restraints, the less chance for bruising. You may, however, have to create your own cuffs, collars, etc. for that purpose. Or something that covers the whole forearm or lower leg, like suspension cuffs, might do the trick.
As far as punishment goes, I'm at something of a loss. I can't think of anything that's guaranteed not to bruise, though I used to use a flogger made of a length of braided cotton rope that I'd unbraided and tied blood knots in the ends of every string. I don't think it ever bruised anyone I used it on, though it was quite sting-y and sometimes left scratches. If you want to avoid even that, unbraid the braided rope but DON'T put blood knots in the ends. It will be extremely soft and good for sensation play, but not very painful (EDIT: It will also tangle if you so much as look at it funny). You might also try toys involving feathers or a wertenberg wheel which, used properly, should not leave any marks on the skin.
But let's face it, there ain't much that's going to have NO chance of leaving bruises. Maybe you could try playing with Tiger Balm or figging?