Well, quelaag is just a long boss fight. It's pretty easy to stay in front of her and roll under her sword strikes since they usually miss anyways. the only attack that you need to be really wary of is when she hugs her spider butt because that means shes about to explode which is usually a 1hitkill. The range is way farther than you think, and if you don't think you can make the distance, just put your shield up. It'll break your guard and you'll take a massive amount of damage but you should be able to live at least.
Also, if you're having problems with the rest of the game try a shield? I'd say Dark wood grain ring would help you out a lot if you insist on just double handing a weapon.
Or if you suck completely, just go full tank. havel/giant armor, giant weapon, giant shield. You'll be able to handle everything with as little skill as possible.
And then there's always the fan favorite.