honestly O&S is one of, if not the absolute most satisfying fight in either souls game. they are tough, its a great battle, and you feel so good when you beat it. to be honest i think if you have gotten the fight to just smough a couple of times you should be able to beat it. the hardest part for me is always killing the first guy when they are both alive. my only real advice (not that either of you asked for it) is to use the pillars and be patient.
What an unbelievably applicable post for what I just did. I've been doing one of EpicNameBro's challenges; pick a class and only use the starting gear and don't level. No Lightning/Fire/Chaos Weapon upgrades, Normal, Magic and Divine are ok. You have to Solo all areas and Bosses as well. I chose a Bandit (Level 4), because I'm digging the Battle Axe right now, and it has a Spider Shield and good starting stats.
Breezing through the first 1/3 of the game with marginally upgraded gear, but I knew S&O would be the first real test. I have most of my gear almost fully upgraded Normal, +15 Shield and Battle Axe, and armor is all at +9 and one at +10, got real lucky with slab drops. So my gear is excellent, but I have no stat scaling so the damage isn't amazing.
I bought a bunch of green blossom and black firebombs (which I have been using a lot on this run). Firebombs can be manually thrown very far, and I used this technique to great effect against the Winged Demons in Anor Londo, who are a pain in the ass up close. Got past the archers and the inside of Anor Londo real easy. Decided to rush past the indoor Giants to the boss door then tackle S&O.
For the Boss fight I chose to take out Ornstein first, I have no problem with Super Ornstein normally, but I think it is much easier to focus on attacking Ornstein while Smough is around when soloing the boss, opposed to vice versa. With Ornstein, he is the most aggressive and mobile anyway, so it is easier to control Smough's movement with the pillars, and avoiding him isn't too hard.
Finding the right time to attack Ornstein while Smough is stalking around is the challenge. The Battle Axe is strong and can stagger with 2 hits when two handed, but it's pretty slow and has very short range, so it's best to hit and run/roll for the first half of the fight. I also threw about 10 Black Firebombs to get another 500 or so extra damage, which pays dividends overall.
I had one almost disastrous moment where I got jammed in a corner, I foolishly attacked Ornstein, he went to swing back so I blocked, but then Smough came in with his rushing attack where he drags the hammer then flips it up. Oh shit; I didn't have enough stamina to block it, so I took all the damage and got launched in the air. I was freaking out on the wakeup, I have S&O waiting to fuck me up and I'm stuck in a corner one hit from death. While I was on the floor I decided to spam roll to my right, I barely missed another attack from Smough, and Ornstein came lunging at me, only to be stopped by a pillar. Amazingly lucky.
I wait about a minute with low health, because I want to make sure I get a safe heal off, so I keep putting distance and pillars between me and S&O. Wait until they both whiff attacks then heal up. Chomp on a green moss and get back into the fight. I keep whittling down Ornstein with single hits after he misses a lunge attack and only when Smough is out of the picture. Get one two hit combo that staggers Ornstein, but I don't get greedy and go for the third because Smough is there to smash me into the ground if I do. Decide to duck a few more hits and finish it off with a black firebomb.
The first half of the fight was definitely the hardest, it took ten minutes to get to the Super Smough section, which was much easier and more manageable. I just stay close and bait his most punishable attacks, which are his 360 swings and straight overhead slams. You can roll toward him to avoid the former, and roll right to avoid the latter, then get in two or three good hits, before he recovers. I had a couple close calls with his butt slam move, but was able to block most of the damage when I wasn't able to outright roll away. Got a couple good stagger chains in, and was able to interrupt his butt slam. I decided to finish Super Smough off with a black firebomb as well, to be completely safe. After about 15 minutes of fighting, I finally beat it. I was elated.
Onto the Lord soul and DLC bosses...