I'm a lightweight too - had some Northern Lights once which...well WOAH - whitie/voices/visuals for 2-3 hours then sleep...
I GUESS the key is to hardly put any in with the baccy, if you don't smoke baccy anyway that'll get you going with VERY little weed - should just get you chilled rather than the phycho "Wallabees wanna screw my hingy-pinglly sour tap radishes whilst pomping in the desert looking at cats which purr in holes filled with desk-tidy morons ish-less hingly wanky thronbisculate gooseberrys..." blah-blah-blah "insane shit" kind of thing going through your head...
(is it normal to get that kind of stuff going on in your head whilst wrecked? You can see why I'd never do shrooms or acid...)