Weird how different playing styles seem to get hung up on different bosses, but for me Gwyn was one of the easier bosses. I had much, much more difficulty with the 4 kings and Ornstein & Smough (which I think I always used an NPC summons for) - and especially the DLC bosses. I never parried Gwyn either - think the key is just to be defensive and not get greedy on the number of swings you take when you get an opening.
Others, like the Iron Golem and the Butterfly or Undead Dragon, it’s hard to imagine killing you other than if you’re not paying attention, but any old Titanite Demon gave me trouble.