Before you even consider going through Blighttown you need poison moss and absolutely need flowering poison moss (Both of which you can get with normal drop rates from the plant guys in the forest). If you've never had a toxic debuff before, it's rough stuff. There's no way to cure it without flowering poison moss.
If you haven't killed the Capra Demon yet (goat skull guy with machettes) then the quickest way is through lower blighttown. It might not be the easiest but you wont have to fight any bosses for this route so there's that. Use the master key through drake valley and go into the tunnel with the ogres. For a quick test to see how difficult the area might be for you, try killing the first one. If he gives you a hard time and you're doing too little damage to him go level up some more (let me know if you would like some info on leveling exploits). If you're good to go, then proceed. Go all the way down to the lift 'til you get to the bottom of the swamp. follow the wall to the left until you come to a dead-end sewer entrance with a bonfire. Rest up and keep following the wall left to a ramp with a few of those mutated slug/people things that shoot fire (For simplicity's sake I'll just call them firebreathers from now on).
Go up the ramp and keep your shield up to block toxic blow darts a tribal-looking guy will be shooting at you. Keep hiding behind your shield until your close enough to kill him. These guys are must-kills. You can try to avoid them, but it's just much easier to deal with them when you can. After that keep going up the scaffolding. It's pretty straight forward from here and I'm assuming you'l want to explore the area so I'll just skip to the next bonfire. Just play it very cautiously since this are can be very frustrating.
Once you reach the bonfire on the giant archway take a breather since you're almost there. keep going forward until you reach some more scaffolding to your left. There should be a ramp on the right that leads to a raised platform with a ladder where a few of mutants will be coming from. Be wary of the area to the left of the ramp as the floor drops out from under you if I remember correctly. The ladder is your target. Go up that and you should be on a small dirt area with a bridge that sways back and forth as you move across it on your right. Don't cross the bridge. Instead follow the dirt wall right unitl you drop down a yard or two to a lower ledge. There should be your shadow set.
Now if you want the iatto, (which is a short samurai sword in the simplest explanation) find your way back to the archway bonfire and then proceed to the swaying bridge. Once you cross it and have dealt with the enemies, there will be a wooden beam that sticks out from the scaffolding to the right. Past that beam there will be a gap that divides the beam from a small raised platform with an item on it. That item is your sword. I highly recommend a running start. By running, I mean hold down the sprint button. If all goes well, you'll have the iatto.
whew... that was a bit longwinded. I'm going by memory so sorry if I was a little vague.
