DON'T whatever you do add weight to the ends of your bow. No pro player I know would recommend that, it will just make the bow completely unmanageable. Weigh it. If it weighs less than about 130 grams its a wee bit light, more than about 150 is heavy. Either way, it's not the problem. The problem is the strings. If you want strings that are good for slap, they will be rubbish for arco. Just the way it is. Part of it is setup, too, but mainly strings. Make your choice, live with it. Sorry, but that's the way it is. Bowing IS much harder than it looks, and using the wrong strings won't help.